Volume 3: The Calculus of Life

Workbook 23.1: Wheels within Wheels

Directives for the Link-Master:

1. Spot the Layers: What is the "Inside" ($g$)? What is the "Outside" ($f$)?
2. Derivative of the Outside: Differentiate the shell, but keep the inside the same!
3. The Multiplier: Multiply your result by the derivative of the inside ($g'$).
4. Box Method: $(\text{Box})^n \to n(\text{Box})^{n-1} \cdot \text{Box}'$.

Part I: Layer Identification

For each function, identify the Inner ($g$) and the Outer ($f$).

$y = (x^2 + 10)^5$

Inner ($g$): $x^2 + 10$
Outer ($f$): $(\text{Box})^5$

$y = \sin(3x)$

Inner ($g$): ...
Outer ($f$): ...

$y = \sqrt{5x - 2}$

Inner ($g$): ...
Outer ($f$): ...

Part II: Applying the Chain Rule

Find the derivative ($y'$) for each function.

$y = (x^2 + 1)^3$

Step 1 (Outer): $3(x^2 + 1)^2$
Step 2 (Inner'): $2x$
Final: $3(x^2 + 1)^2 \cdot 2x = 6x(x^2 + 1)^2$

$y = (4x - 5)^{10}$

...

$y = \sin(x^2)$

Note: Derivative of $\sin$ is $\cos$.
...
The Logic Check:

If you have $y = (2x + 5)^1$... what is the derivative? Does the Chain Rule give you the same answer as the Power Rule? Explain.

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Part III: The Gear Ratio

A machine has an inner gear ($u$) and an outer gear ($y$).
$y = u^2$ (The outer speed is the square of the inner).
$u = 5x + 1$ (The inner speed depends on the pedal $x$).
Find the rate of change of the whole machine ($\frac{dy}{dx}$).

$\frac{dy}{du} = 2u = 2(5x + 1)$
$\frac{du}{dx} = 5$
Total = ...

Part IV: The Challenge (The Triple Link)

Wheels within Wheels within Wheels

Find the derivative of $y = \sin((x^2 + 1)^3)$.
This has three layers!
1. Sine (Outside)
2. Cube (Middle)
3. $(x^2 + 1)$ (Inside)

$\cos((x^2+1)^3) \cdot 3(x^2+1)^2 \cdot 2x = ...$

Part V: Transmission (The Echad Extension)

Teacher Log: The Nested Boxes

Objective: Explain the Chain Rule to a younger sibling using boxes.

The Activity:
1. Put a toy in a small box. Put the small box in a large box.
2. Tell them: "If I move the large box 1 foot, the toy moves 1 foot. But if I also move the small box *inside* the large one, the toy moves even more!"

The Lesson: "Total change is the Outer move plus the Inner move. In math, we multiply them to find the new speed."


Response: ___________________________________________________________

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