source_difficulty: direct

review_outcome: accept

status: pass

sharp: pass

rigorous: pass

consistent: pass

learnable: pass

notes: Native audio understanding directly distinguishes one short spoken option.

current_markdown:
# Agent Chain of Thought: cal-0002

> Scene: `education_lecture` · Actual tool calls: 0 · Tool-count bucket: `0`

## Question

Which option is spoken in the lecture clip?

## Choices

A. And you know, near the minimum of the potential, the potential is roughly quadratic in general.
B. We'll typically go the first and the second and sometimes make some remarks about these things.
C. IT should go into n1. But the only state in n1 is k0.
D. So the superscript is telling you what order in lambda you are working-- to what accuracy.

## Response

Problem analysis: The audible evidence shows that the first option is spoken verbatim in this short lecture clip, while the distinctive terms from the other options are absent. This means the first option is uniquely supported. The evidence is sufficient because the short original audio directly resolves the exact-wording comparison. Therefore, I will answer with the first option.

Answer: **And you know, near the minimum of the potential, the potential is roughly quadratic in general.**

verdict: unreviewed

sharp: unreviewed

rigorous: unreviewed

consistent: unreviewed

learnable: unreviewed


notes: The single ASR result contains the selected option's distinctive clause.

current_markdown:
# Agent Chain of Thought: cal-0001

> Scene: `education_lecture` · Actual tool calls: 1 · Tool-count bucket: `1`

## Question

Which option is spoken in the lecture clip?

## Choices

A. So, what is the entropy telling us?
B. Let's figure how to solve her problem!
C. Let's start by asking "what is information?"
D. Hmm. What do those fractional bits mean?

## Response

Problem analysis: The choices differ by exact wording, and the original clip alone does not give me enough confidence to distinguish every clause. The required evidence is a transcript that can be compared with each option. Therefore, I will call asr.transcribe on the clip.

<Tool_call>

```json
{
  "type": "tool_call",
  "tool": "asr",
  "operation": "transcribe",
  "audio": [
    "input:0"
  ],
  "arguments": {
    "detail": "text"
  }
}
```

</Tool_call>

Tool output:

```json
{
  "type": "tool_result",
  "name": "asr",
  "operation": "transcribe",
  "result": {
    "usable": true,
    "data": {
      "language": "English",
      "text": "Let's start by asking, \"What is information?\" From our engineering."
    }
  }
}
```

Evidence and completeness check: The tool result shows that the transcript contains the third option's distinctive wording exactly. This means the third option is uniquely supported and the competing clauses are not. The evidence is sufficient because the transcription directly resolves the only material uncertainty. Therefore, I will answer with the third option.

Answer: **Let's start by asking "what is information?"**


bucket: n

notes: The solver-visible focused ASR uniquely supports the selected option despite omitting its final word.

notes: A private 8.5–10.8 second Qwen3-Omni-Thinking caption audit heard the complete question; that audit is not solver-visible evidence.

current_markdown:
# Agent Chain of Thought: cal-0005

> Scene: `meeting_collaboration` · Actual tool calls: 3 · Tool-count bucket: `n`

## Question

What complete question is asked immediately before the second distinct speaker in the clip first responds?

## Choices

A. Who would like to go first?
B. What is your favorite animal?
C. Where should we put it?
D. Who has the remote?

## Response

Problem analysis: The answer depends on the utterance immediately before the second distinct speaker first responds. The required evidence is the first speaker-change boundary followed by the content just before it. Therefore, I will call speaker_diarization.analyze_speakers on the clip.

<Tool_call>

```json
{
  "type": "tool_call",
  "tool": "speaker_diarization",
  "operation": "analyze_speakers",
  "audio": [
    "input:0"
  ],
  "arguments": {
    "max_analysis_seconds": 600
  }
}
```

</Tool_call>

Tool output:

```json
{
  "type": "tool_result",
  "name": "speaker_diarization",
  "operation": "analyze_speakers",
  "result": {
    "usable": true,
    "data": {
      "speaker_segments": [
        {
          "duration": 0.4,
          "end": 0.4,
          "mean_activity_probability": 0.996899,
          "speaker": "speaker_0",
          "speaker_slot": 0,
          "start": 0.0
        },
        {
          "duration": 0.4,
          "end": 1.6,
          "mean_activity_probability": 0.917791,
          "speaker": "speaker_0",
          "speaker_slot": 0,
          "start": 1.2
        },
        {
          "duration": 0.96,
          "end": 3.6,
          "mean_activity_probability": 0.957829,
          "speaker": "speaker_0",
          "speaker_slot": 0,
          "start": 2.64
        },
        {
          "duration": 1.6,
          "end": 6.0,
          "mean_activity_probability": 0.995854,
          "speaker": "speaker_0",
          "speaker_slot": 0,
          "start": 4.4
        },
        {
          "duration": 2.08,
          "end": 8.64,
          "mean_activity_probability": 0.978823,
          "speaker": "speaker_0",
          "speaker_slot": 0,
          "start": 6.56
        },
        {
          "duration": 1.36,
          "end": 10.32,
          "mean_activity_probability": 0.961756,
          "speaker": "speaker_0",
          "speaker_slot": 0,
          "start": 8.96
        },
        {
          "duration": 1.12,
          "end": 10.8,
          "mean_activity_probability": 0.862757,
          "speaker": "speaker_1",
          "speaker_slot": 1,
          "start": 9.68
        },
        {
          "duration": 0.72,
          "end": 11.52,
          "mean_activity_probability": 0.90132,
          "speaker": "speaker_0",
          "speaker_slot": 0,
          "start": 10.8
        },
        {
          "duration": 0.32,
          "end": 17.6,
          "mean_activity_probability": 0.765541,
          "speaker": "speaker_2",
          "speaker_slot": 2,
          "start": 17.28
        },
        {
          "duration": 0.4,
          "end": 19.52,
          "mean_activity_probability": 0.787697,
          "speaker": "speaker_2",
          "speaker_slot": 2,
          "start": 19.12
        }
      ],
      "overlap_segments": [
        {
          "duration": 0.64,
          "end": 10.32,
          "num_concurrent_speakers": 2,
          "speakers": [
            "speaker_0",
            "speaker_1"
          ],
          "start": 9.68
        }
      ],
      "estimated_speaker_count": 3
    }
  }
}
```

Evidence and completeness check: The tool result shows that the first segment assigned to speaker_1 starts at 9.68 seconds and is preceded by speaker_0 from 8.96 to 9.68 seconds. This means the requested question must lie in that immediately preceding interval. The evidence is not yet sufficient because diarization identifies speakers and timing but not the spoken words. Therefore, I will call audio_navigation.crop on the 8.96–9.68 second interval.

<Tool_call>

```json
{
  "type": "tool_call",
  "tool": "audio_navigation",
  "operation": "crop",
  "audio": [
    "input:0"
  ],
  "arguments": {
    "start_seconds": 8.96,
    "end_seconds": 9.68
  }
}
```

</Tool_call>

Tool output:

```json
{
  "type": "tool_result",
  "name": "audio_navigation",
  "operation": "crop",
  "result": {
    "usable": true,
    "data": {
      "artifact": {
        "ref": "artifact:e5810c9940fbccc31ca7f9b396a633ec70851a5e4c83b0d5f746bcdb5e27ed49.wav",
        "channels": 1,
        "duration_seconds": 0.72,
        "end_seconds": 9.68,
        "frames": 11520,
        "media_type": "audio/wav",
        "sample_rate": 16000,
        "sha256": "e5810c9940fbccc31ca7f9b396a633ec70851a5e4c83b0d5f746bcdb5e27ed49",
        "start_seconds": 8.96
      }
    }
  }
}
```

Evidence and completeness check: The tool result shows that the selected interval has been isolated as a short audio artifact. This means the candidate question can now be inspected without the surrounding meeting audio. The evidence is not yet sufficient because the crop result contains no lexical content to compare with the choices. Therefore, I will call asr.transcribe on the cropped artifact.

<Tool_call>

```json
{
  "type": "tool_call",
  "tool": "asr",
  "operation": "transcribe",
  "audio": [
    "artifact:e5810c9940fbccc31ca7f9b396a633ec70851a5e4c83b0d5f746bcdb5e27ed49.wav"
  ],
  "arguments": {
    "detail": "text"
  }
}
```

</Tool_call>

Tool output:

```json
{
  "type": "tool_result",
  "name": "asr",
  "operation": "transcribe",
  "result": {
    "usable": true,
    "data": {
      "language": "English",
      "text": "So who would like to go?"
    }
  }
}
```

Evidence and completeness check: The tool result shows the focused transcript, 'So who would like to go?' This means the utterance uniquely matches the first choice despite omitting its final word. The evidence is sufficient because no other choice shares this wording or intent. Therefore, I will answer with the first option.

Answer: **Who would like to go first?**


primary_bucket: hard

source_difficulty: edge

notes: All five visible calls have successful real execution receipts; no failed tool behavior is retained.

notes: The broad timestamped ASR localizes both quotations, and both fresh short crops are independently transcribed before the answer.

notes: Qwen3-Omni-Thinking captioned only the already-localized short clips for editor assistance; the final solver also received and listened to the fresh focused clips.

current_markdown:
# Agent Chain of Thought: cal-0004-repair-4

> Scene: `education_lecture` · Actual tool calls: 5 · Tool-count bucket: `n`

## Question

Which quoted phrase is spoken earlier in this 15-minute lecture excerpt?
Phrase A: “And that's going to be our slope.”
Phrase B: “All right, maybe I should draw it just a bit lower.”
Answer with Phrase A or Phrase B.

## Choices

A. Phrase A
B. Phrase B

## Response

Problem analysis: The answer depends on the relative position of two exact phrases across a 15-minute recording. The required evidence is a timestamped transcript that can locate both quotations without sending the 900-second input to an operation capped at 600 seconds. Therefore, I will call asr.transcribe with timestamp detail.

<Tool_call>

```json
{
  "type": "tool_call",
  "tool": "asr",
  "operation": "transcribe",
  "audio": [
    "input:0"
  ],
  "arguments": {
    "detail": "timestamps"
  }
}
```

</Tool_call>

Tool output:

```json
{
  "type": "tool_result",
  "name": "asr",
  "operation": "transcribe",
  "result": {
    "usable": true,
    "data": {
      "language": "English",
      "text": "The following content is provided under a Creative Commons license. Your support will help MIT OpenCourseWare continue to offer high-quality educational resources for free. To make a donation or to view additional materials from hundreds of MIT courses, visit MIT OpenCourseWare at ocw.mit.edu. So again, welcome to 1801. We're getting started today with what we're calling Unit One, highly imaginative topic, highly imaginative title, and it's differentiation. So let me first tell you briefly what's in store in the next couple of weeks. The main topic today is what is a derivative, and we're going to look at this from several different points of view. And the first one is the geometric interpretation, and that's what we'll spend most of today on. And then we'll also talk about a physical interpretation of what a derivative is. And then there's going to be something else which I guess is maybe the reason why calculus is so fundamental, why we always start with it. In most science and engineering schools, which is the importance of derivatives of this to all measurements. So that means pretty much every place that means in science, in engineering, in economics, in political science, et cetera, polling, lots of commercial applications, just just about everything. Now, so that's what we'll be getting started with, and then there's another thing that we're going to do in this unit, which is we're going to explain how to differentiate any. So how to differentiate any function you know.And that's kind of a tall order, but let me just give you an example. If you want to take the derivative, this we'll see today is the notation for the derivative of something, of some messy function like e to the x arc tan of x. We'll work this out by the end of this unit. All right. So anything you can think of, anything you can write down, we can differentiate it. All right. So that's what we're going to do. And today, as I said, we're going to spend most of our time on this geometric interpretation. So let's let's begin with that. So here we go with the geometric interpretation of derivatives. And what we're going to do is just ask the geometric problem of finding the tangent line to some graph of some function at some point, which is say x zero y. So that's the problem that we're addressing here. Um, guess I should probably turn this off. All right. So here's our problem, and now let me show you the solution. So well let's graph the function. So let's say here is its graph, and here's some point. All right. Maybe I should draw it just a bit lower so that I don't. All right. So here's a point P. Maybe it's above the point x zero. X zero by the way, this was supposed to be an x zero that was the some fixed place on the x axis. And now in order to perform this this my feet, I will um use another color of chalk. How about red? Okay. So so here it is. Here's the tangent line. Well, not quite straight close enough. All right. I did it. All right. That's yeah. That's the geometric problem. I achieved what I wanted to do, and uh.It's kind of an interesting question which unfortunately I can't solve for you in this class which is how did I do that that is how physically did I manage to know what to do to draw this tangent line but that's what geometric problems are like we visualize it we can figure it out somewhere in our brains it happens and the task that we have now is to figure out how to do it analytically to do it in a way that a machine could do just as well as I did in drawing this tangent line so so what do we learn in high school about what a tangent line is well a tangent line has an equation and any line through point has the equation y minus y zero is equal to m the slope times x minus x zero so so here's the the equation for that line and now there are two pieces of information that we're going to need to work out what the line is the first one is the point that's that point P there and to specify P given given x we need to know the the the level of y which is of course just f of x zero now that's that's not a calculus problem but anyway that's a very important part of the process so that's the first thing we need to know and the second thing we need to know is the slope and that's this number m and in calculus we have another name for it we call it f prime of x zero namely the derivative of f so that's the calculus part that's the tricky part and that's the part that we have to discuss now so just to make that explicit here I'm going to make a definition which is that f prime of x zero which is known as the derivative of f at x zero right is the slope of the tangent line to y equals f of x at the point let's just call it P all right soSo that's what it is, but still I haven't made any progress in figuring out any better how I drew that line. So I have to say something that's more concrete because I want to be able to cook up what these numbers are. I have to figure out what this number m is. And one way of thinking about that, let me just try it is. So I certainly am taking for granted that in sort of non-calculus part that I know what a line through a point is. So I know this equation. But another possibility might be, you know this line here. How do I know? Well unfortunately I didn't draw it quite straight, but there it is. How do I know that this orange line is not a tangent line, but this other line is a tangent line? Well, it's it's actually not so obvious. And but I'm going to describe it a little bit. It's it's not really the fact this thing crosses at some other place, which is this point Q. But it's not really the fact that the thing crosses at two places because the line could be wiggly, the curve could be wiggly, and it could cross back and forth a number of times. That's not what distinguishes the tangent line. So I'm going to have to somehow grasp this and first do it in language. And it's the following idea, it's that if you take this orange line which is called a secant line, and you think of the Q, the point Q is getting closer and closer to P, then the slope of that line will get closer and closer to the slope of the red line. And if we draw a close enough, then that's going to be the correct line. So that's really what I did sort of in my brain when I drew that first line. And so that's the way I'm going to articulate it first. Now so the tangent line is equal to the limit of what so called secant lines PQ as Q tends to P. And here we're thinking of P is being fixed. And Q is very. Alright so so that's the the again this is still a geometric discussion, but now we're going to be able to put symbols and formulas to this computation and we'll be able to to work out.Formula is in any example. So, so let's do that. So first of all, I'm going to write out these points P and Q again. So maybe we'll put P here and Q here. And I'm thinking of this line through them. I guess it was orange, so we'll leave it as orange. Right? And now I want to compute its slope. And so this gradually will do this in two steps, and these steps will introduce us to the basic notations which are used throughout calculus, including multivariable calculus across the board. So the first notation that's used is you imagine here's the x-axis underneath, and here's the x zero, the location directly below the point P. And we're traveling here a horizontal distance, which is denoted by delta x. So that's delta x, so called. And we could also call it the change in x. All right. So that's one thing we want to measure in order to get the slope of this line PQ. And the other thing is this height. So that's this distance here, which we denote delta f, which is the change in f. And then the slope is just the ratio delta f over delta x. So this is the slope of the of the secant. And the process I just described over here with this limit applies not just to the whole line itself, but also in particular to its slope. And the way we write that is the limit as delta x goes to zero, and that's going to be our slope. So this is the slope of the tangent line. Okay, now this is still a little a little general, and I'm going I want to work out a more usable form here. I want to work out a better formula for this. And in order to do that, I'm going to write delta f, the numerator more explicitly here, the change in f. So remember that the point P is the point x zero f of x zero.All right, that's what we got from our formula for the point. And, in order to compute these distances, and in particular the vertical distance here, I'm going to have to get a formula for q as.",
      "timestamp_windows": [
        {
          "text": "The following content is provided under Creative Commons license Your support will help MIT OpenCourseWare continue to",
          "start_seconds": 0.08,
          "end_seconds": 6.64
        },
        {
          "text": "offer highquality educational resources for free To make a donation or to view additional materials from hundreds",
          "start_seconds": 6.72,
          "end_seconds": 13.2
        },
        {
          "text": "of MIT courses visit MIT OpenCourseWare at ocwmitedu again welcome to 1801 We're getting started today with",
          "start_seconds": 13.2,
          "end_seconds": 27.6
        },
        {
          "text": "what we're calling Unit One highly imaginative topic highly imaginative title and it's differentiation So let me",
          "start_seconds": 28.72,
          "end_seconds": 44.4
        },
        {
          "text": "first tell you briefly what's in store in next couple of weeks The main topic today is",
          "start_seconds": 44.4,
          "end_seconds": 52.4
        },
        {
          "text": "what is a derivative and we're going to look at this from several different points of view",
          "start_seconds": 53.04,
          "end_seconds": 70.96
        },
        {
          "text": "And the first one is the geometric interpretation that's what spend most of today on And then",
          "start_seconds": 71.84,
          "end_seconds": 84.32
        },
        {
          "text": "we'll also talk about physical interpretation of what a derivative is And then there's going to be",
          "start_seconds": 85.04,
          "end_seconds": 103.52
        },
        {
          "text": "something else which I guess is maybe the reason why calculus is so fundamental why we always",
          "start_seconds": 103.52,
          "end_seconds": 109.36
        },
        {
          "text": "start with it In most science and engineering schools which is the importance of derivatives of this",
          "start_seconds": 109.36,
          "end_seconds": 121.6
        },
        {
          "text": "to all measurements So that means pretty much every place that means in science in engineering in",
          "start_seconds": 122.0,
          "end_seconds": 136.08
        },
        {
          "text": "economics in political science cetera polling lots of commercial applications just just about everything Now so that's",
          "start_seconds": 136.48,
          "end_seconds": 151.84
        },
        {
          "text": "what we'll be getting started with and then there's another thing that we're going to do in",
          "start_seconds": 151.84,
          "end_seconds": 157.36
        },
        {
          "text": "this unit which is we're going to explain how to differentiate any how to differentiate any function",
          "start_seconds": 157.36,
          "end_seconds": 172.56
        },
        {
          "text": "you know And that's kind of tall order but let just give you an example If you",
          "start_seconds": 172.56,
          "end_seconds": 186.857
        },
        {
          "text": "want to take derivative this we'll see today is the notation for the derivative of something of",
          "start_seconds": 186.857,
          "end_seconds": 191.977
        },
        {
          "text": "some messy function like e to the x arc tan of x We'll work this out by",
          "start_seconds": 191.977,
          "end_seconds": 202.457
        },
        {
          "text": "the end of this unit All right So anything you can think of anything you can write",
          "start_seconds": 202.457,
          "end_seconds": 208.617
        },
        {
          "text": "down we can differentiate All right So that's what we're going do And today as I said",
          "start_seconds": 208.617,
          "end_seconds": 217.657
        },
        {
          "text": "we're going spend most of our time on this geometric interpretation So let's let's begin with that",
          "start_seconds": 218.297,
          "end_seconds": 226.617
        },
        {
          "text": "So here we go with the geometric interpretation derivatives And what we're going to do is just",
          "start_seconds": 230.457,
          "end_seconds": 249.817
        },
        {
          "text": "ask the geometric problem of finding tangent line to graph of some function at some point which",
          "start_seconds": 249.897,
          "end_seconds": 271.657
        },
        {
          "text": "is say x zero y So that's the problem that we're addressing here Um guess I should",
          "start_seconds": 271.657,
          "end_seconds": 279.257
        },
        {
          "text": "probably turn this off All right So here's our problem and now let me show you the",
          "start_seconds": 279.417,
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        },
        {
          "text": "solution So well let's graph function So let's say here is its graph and here's some point",
          "start_seconds": 287.657,
          "end_seconds": 301.977
        },
        {
          "text": "All right Maybe I should draw just a bit lower so that I don't right So here's",
          "start_seconds": 302.857,
          "end_seconds": 310.217
        },
        {
          "text": "a point P Maybe it's above the point x zero X zero by way this was supposed",
          "start_seconds": 310.217,
          "end_seconds": 318.777
        },
        {
          "text": "to be an x zero that was the some fixed place on the x axis And now",
          "start_seconds": 318.777,
          "end_seconds": 328.457
        },
        {
          "text": "in order to perform this this my feet I will use another color of chalk How about",
          "start_seconds": 329.097,
          "end_seconds": 337.417
        },
        {
          "text": "red Okay So so here it is Here's the tangent line Well not quite straight close enough",
          "start_seconds": 337.417,
          "end_seconds": 345.497
        },
        {
          "text": "All I did it All right That's yeah That's the geometric problem I achieved what wanted do",
          "start_seconds": 346.297,
          "end_seconds": 353.737
        },
        {
          "text": "and uh It's kind of an interesting question which unfortunately I can't solve for you in this",
          "start_seconds": 354.457,
          "end_seconds": 361.318
        },
        {
          "text": "class which is how did I do that that is how physically did I manage to know",
          "start_seconds": 361.318,
          "end_seconds": 365.638
        },
        {
          "text": "what to do to draw this tangent line but that's what geometric problems are like we visualize",
          "start_seconds": 366.038,
          "end_seconds": 372.278
        },
        {
          "text": "it we can figure out somewhere our brains it happens and the task that we have now",
          "start_seconds": 372.278,
          "end_seconds": 377.958
        },
        {
          "text": "is to figure out how to do it analytically to do it in way that a machine",
          "start_seconds": 378.358,
          "end_seconds": 387.398
        },
        {
          "text": "could do just as well as I did in drawing this tangent line so so what do",
          "start_seconds": 387.558,
          "end_seconds": 396.438
        },
        {
          "text": "we learn in high school about what tangent line is well a tangent line has an equation",
          "start_seconds": 396.438,
          "end_seconds": 403.318
        },
        {
          "text": "and any line through point has the equation y minus y zero is equal to m the",
          "start_seconds": 403.878,
          "end_seconds": 409.478
        },
        {
          "text": "slope times x minus x zero so here's the the equation for that line and now there",
          "start_seconds": 409.478,
          "end_seconds": 420.438
        },
        {
          "text": "are two pieces of information we're going to need to work out what line is first one",
          "start_seconds": 420.438,
          "end_seconds": 428.598
        },
        {
          "text": "is the point that's that point P there and to specify P given given x we need",
          "start_seconds": 428.678,
          "end_seconds": 437.078
        },
        {
          "text": "to know the the level of y which is of course just f of x zero now",
          "start_seconds": 437.078,
          "end_seconds": 442.678
        },
        {
          "text": "that's that's not calculus problem but anyway that's very important part of the process so that's first",
          "start_seconds": 442.678,
          "end_seconds": 449.558
        },
        {
          "text": "thing we need to know and the second thing we need to know is slope and that's",
          "start_seconds": 449.558,
          "end_seconds": 460.438
        },
        {
          "text": "this number m and in calculus we have another name for we call it f prime of",
          "start_seconds": 460.438,
          "end_seconds": 467.398
        },
        {
          "text": "x zero namely the derivative of f so that's calculus part that's the tricky part and that's",
          "start_seconds": 467.398,
          "end_seconds": 474.998
        },
        {
          "text": "the part that we have to discuss now so just to make that explicit here I'm going",
          "start_seconds": 474.998,
          "end_seconds": 481.958
        },
        {
          "text": "to make definition which is that f prime of x zero which is known as the derivative",
          "start_seconds": 481.958,
          "end_seconds": 488.758
        },
        {
          "text": "of at x zero right is slope of the tangent line to y equals f of x",
          "start_seconds": 488.918,
          "end_seconds": 515.878
        },
        {
          "text": "at the point let's just call P all right so So that's what it is but still",
          "start_seconds": 516.918,
          "end_seconds": 535.588
        },
        {
          "text": "I haven't made any progress in figuring out any better how I drew that line So I",
          "start_seconds": 535.588,
          "end_seconds": 541.828
        },
        {
          "text": "have to say something that's more concrete because I want to be able to cook up what",
          "start_seconds": 541.828,
          "end_seconds": 546.868
        },
        {
          "text": "these numbers are I have to figure out what this number m is And one way of",
          "start_seconds": 546.868,
          "end_seconds": 552.708
        },
        {
          "text": "thinking about that let me just try is So certainly am taking for granted that in sort",
          "start_seconds": 552.708,
          "end_seconds": 559.828
        },
        {
          "text": "noncalculus part that I know what line through point is So I know this equation But another",
          "start_seconds": 559.828,
          "end_seconds": 565.348
        },
        {
          "text": "possibility might be know this line here How do I know unfortunately I didn't draw it straight",
          "start_seconds": 565.348,
          "end_seconds": 571.108
        },
        {
          "text": "but there it is How do I know that this orange line is not a tangent line",
          "start_seconds": 571.188,
          "end_seconds": 577.508
        },
        {
          "text": "but this other line is a tangent line Well it's it's actually not so obvious And but",
          "start_seconds": 578.228,
          "end_seconds": 593.668
        },
        {
          "text": "I'm going describe it little bit It's it's not really the fact this thing crosses at some",
          "start_seconds": 593.668,
          "end_seconds": 599.828
        },
        {
          "text": "other place which is this point Q But it's not really the fact that the thing crosses",
          "start_seconds": 599.828,
          "end_seconds": 606.308
        },
        {
          "text": "at two places because the line could be wiggly the curve could be wiggly and it could",
          "start_seconds": 606.308,
          "end_seconds": 610.228
        },
        {
          "text": "cross back and forth a number of times That's not what distinguishes the tangent line So I'm",
          "start_seconds": 610.308,
          "end_seconds": 617.828
        },
        {
          "text": "going to have to somehow grasp this and first do it in language And it's the following",
          "start_seconds": 617.828,
          "end_seconds": 625.108
        },
        {
          "text": "idea it's that if you take this orange line which is called secant line and you think",
          "start_seconds": 625.108,
          "end_seconds": 636.068
        },
        {
          "text": "of the Q the point Q is getting closer and closer to P then the slope of",
          "start_seconds": 636.228,
          "end_seconds": 642.388
        },
        {
          "text": "that line will get closer closer the slope of the red line And if we draw a",
          "start_seconds": 642.388,
          "end_seconds": 651.028
        },
        {
          "text": "close enough then that's going be the correct line So that's really what I did sort of",
          "start_seconds": 651.028,
          "end_seconds": 656.708
        },
        {
          "text": "in my brain when I drew that first line And so that's the way I'm going to",
          "start_seconds": 656.708,
          "end_seconds": 659.828
        },
        {
          "text": "articulate it first Now so the tangent line is equal to limit of what so called secant",
          "start_seconds": 659.828,
          "end_seconds": 674.788
        },
        {
          "text": "lines PQ as Q tends to P And here we're thinking of P is being fixed And",
          "start_seconds": 674.788,
          "end_seconds": 688.388
        },
        {
          "text": "Q is very Alright so so that's the the again this is still geometric discussion but now",
          "start_seconds": 688.788,
          "end_seconds": 699.508
        },
        {
          "text": "we're going to be able put symbols and formulas to this computation and we'll be able to",
          "start_seconds": 699.988,
          "end_seconds": 705.508
        },
        {
          "text": "work out Formula is in any example So so let's do that So first of all I'm",
          "start_seconds": 706.468,
          "end_seconds": 721.901
        },
        {
          "text": "going to write out these points P and Q again So maybe we'll put P here and",
          "start_seconds": 721.901,
          "end_seconds": 728.781
        },
        {
          "text": "Q here And I'm thinking this line through them I guess it was orange so leave it",
          "start_seconds": 728.781,
          "end_seconds": 735.101
        },
        {
          "text": "as orange Right And now I want to compute its slope And so this gradually will do",
          "start_seconds": 735.821,
          "end_seconds": 746.381
        },
        {
          "text": "this in two steps and these steps will introduce us to the basic notations which used throughout",
          "start_seconds": 746.381,
          "end_seconds": 751.421
        },
        {
          "text": "calculus including multivariable calculus across the board So the first notation that's used is you imagine here's",
          "start_seconds": 751.421,
          "end_seconds": 760.861
        },
        {
          "text": "the xaxis underneath and here's the x zero the location directly below the point P And we're",
          "start_seconds": 760.861,
          "end_seconds": 768.701
        },
        {
          "text": "traveling here a horizontal distance which is denoted by delta x So that's delta x so called",
          "start_seconds": 768.701,
          "end_seconds": 778.221
        },
        {
          "text": "And we could also call the change in x right So that's one thing we want measure",
          "start_seconds": 779.421,
          "end_seconds": 789.821
        },
        {
          "text": "in order to get the slope of this line PQ And the other thing is this height",
          "start_seconds": 789.821,
          "end_seconds": 794.301
        },
        {
          "text": "So that's this distance here which we denote delta f which is the change in f And",
          "start_seconds": 794.861,
          "end_seconds": 802.621
        },
        {
          "text": "then slope is just the ratio delta f over delta x So this is the slope of",
          "start_seconds": 802.701,
          "end_seconds": 811.981
        },
        {
          "text": "the of the secant And process I just described over here with this limit applies not just",
          "start_seconds": 811.981,
          "end_seconds": 825.741
        },
        {
          "text": "to the whole line itself but also in particular to its slope And way we write that",
          "start_seconds": 825.741,
          "end_seconds": 830.461
        },
        {
          "text": "is the limit as delta x goes to zero and that's going to be our slope So",
          "start_seconds": 830.541,
          "end_seconds": 836.621
        },
        {
          "text": "this is the slope of the tangent line Okay now this is still a little little general",
          "start_seconds": 836.621,
          "end_seconds": 859.821
        },
        {
          "text": "and I'm going want to work out a more usable form here I want work out better",
          "start_seconds": 859.901,
          "end_seconds": 867.341
        },
        {
          "text": "formula for this And in order to do that I'm going to write delta f the numerator",
          "start_seconds": 867.341,
          "end_seconds": 874.141
        },
        {
          "text": "more explicitly here change in f So remember that point P is the point x zero f",
          "start_seconds": 874.221,
          "end_seconds": 883.581
        },
        {
          "text": "of x zero All right that's what we got from our formula for the point And in",
          "start_seconds": 883.581,
          "end_seconds": 892.83
        },
        {
          "text": "order to compute these distances and in particular the vertical distance here I'm going have get formula",
          "start_seconds": 892.83,
          "end_seconds": 899.07
        },
        {
          "text": "for q as",
          "start_seconds": 899.07,
          "end_seconds": 899.95
        }
      ],
      "segments_total": 1,
      "words_total": 1601
    }
  }
}
```

Evidence and completeness check: The tool result shows the drawing phrase near 303 seconds and the slope phrase near 831 seconds. This means Phrase B is provisionally earlier and both decisive regions are localized. The evidence is not yet sufficient because the result spans the full recording and each quotation still needs a fresh local check. Therefore, I will call audio_navigation.crop on short windows around both locations.

<Tool_call>

```json
{
  "type": "tool_call",
  "tool": "audio_navigation",
  "operation": "crop",
  "audio": [
    "input:0"
  ],
  "arguments": {
    "start_seconds": 298.0,
    "end_seconds": 313.0
  },
  "batch_index": 0
}
```

</Tool_call>

Tool output:

```json
{
  "batch_index": 0,
  "type": "tool_result",
  "name": "audio_navigation",
  "operation": "crop",
  "result": {
    "usable": true,
    "data": {
      "artifact": {
        "ref": "artifact:033182317d3e42ad57b1d327382c57e208113ea3691a0d13d6fb420f8191b2a4.wav",
        "channels": 1,
        "duration_seconds": 15.0,
        "end_seconds": 313.0,
        "frames": 240000,
        "media_type": "audio/wav",
        "sample_rate": 16000,
        "sha256": "033182317d3e42ad57b1d327382c57e208113ea3691a0d13d6fb420f8191b2a4",
        "start_seconds": 298.0
      }
    }
  }
}
```

<Tool_call>

```json
{
  "type": "tool_call",
  "tool": "audio_navigation",
  "operation": "crop",
  "audio": [
    "input:0"
  ],
  "arguments": {
    "start_seconds": 829.0,
    "end_seconds": 840.0
  },
  "batch_index": 1
}
```

</Tool_call>

Tool output:

```json
{
  "batch_index": 1,
  "type": "tool_result",
  "name": "audio_navigation",
  "operation": "crop",
  "result": {
    "usable": true,
    "data": {
      "artifact": {
        "ref": "artifact:835eadfbdd7cba8151a3133e5480a1c6015583a23bb02c68507c054d7d7057b3.wav",
        "channels": 1,
        "duration_seconds": 11.0,
        "end_seconds": 840.0,
        "frames": 176000,
        "media_type": "audio/wav",
        "sample_rate": 16000,
        "sha256": "835eadfbdd7cba8151a3133e5480a1c6015583a23bb02c68507c054d7d7057b3",
        "start_seconds": 829.0
      }
    }
  }
}
```

Evidence and completeness check: The tool result shows that the 298–313 second and 829–840 second regions are now available as two short artifacts. This means each candidate quotation can be checked directly without the rest of the lecture. The evidence is not yet sufficient because crop artifacts do not themselves expose the spoken words. Therefore, I will call asr.transcribe on both artifacts in one batch.

<Tool_call>

```json
{
  "type": "tool_call",
  "tool": "asr",
  "operation": "transcribe",
  "audio": [
    "artifact:033182317d3e42ad57b1d327382c57e208113ea3691a0d13d6fb420f8191b2a4.wav"
  ],
  "arguments": {
    "detail": "text"
  },
  "batch_index": 0
}
```

</Tool_call>

Tool output:

```json
{
  "batch_index": 0,
  "type": "tool_result",
  "name": "asr",
  "operation": "transcribe",
  "result": {
    "usable": true,
    "data": {
      "language": "English",
      "text": "So let's say here's its graph, and here's some point. All right, maybe I should draw it just a bit lower so that I don't. All right, so here's a point P. Maybe it's."
    }
  }
}
```

<Tool_call>

```json
{
  "type": "tool_call",
  "tool": "asr",
  "operation": "transcribe",
  "audio": [
    "artifact:835eadfbdd7cba8151a3133e5480a1c6015583a23bb02c68507c054d7d7057b3.wav"
  ],
  "arguments": {
    "detail": "text"
  },
  "batch_index": 1
}
```

</Tool_call>

Tool output:

```json
{
  "batch_index": 1,
  "type": "tool_result",
  "name": "asr",
  "operation": "transcribe",
  "result": {
    "usable": true,
    "data": {
      "language": "English",
      "text": "And the way we write that is the limit, as delta x goes to zero, and that's going to be our slope. So this is the slope, of the tangent line."
    }
  }
}
```

Evidence and completeness check: The tool result shows that the first focused transcript contains Phrase B and the second contains Phrase A. This means both quotations are verified on localized audio and their source windows preserve the order 303 seconds before 831 seconds. The evidence is sufficient because the broad localization and both independent focused checks agree. Therefore, I will answer Phrase B.

Answer: **Phrase B**