Volume 3: The Calculus of Life

Workbook 23.3: Implicit Differentiation

Directives for the Searcher:

1. Differentiate Both Sides: Apply $\frac{d}{dx}$ to every term.
2. The Y-Witness: Whenever you differentiate $y$, multiply by $\frac{dy}{dx}$.
3. Group the Primes: Move every term containing $\frac{dy}{dx}$ to the left.
4. Isolate: Factor out the $\frac{dy}{dx}$ and solve the equation.

Part I: Basic Secret Searches

Find $\frac{dy}{dx}$ for each equation.

$x^2 + y^2 = 36$

$\frac{d}{dx}[x^2] + \frac{d}{dx}[y^2] = \frac{d}{dx}[36]$
$2x + 2y \cdot \frac{dy}{dx} = 0$
Solve for $\frac{dy}{dx}$: ...

$y^3 = x + 10$

$3y^2 \cdot \frac{dy}{dx} = 1$
$\frac{dy}{dx} = ...$

$x^2 + 5y = 100$

...

Part II: Multi-Term Secrets

$x^2 - y^2 = 1$ (A Hyperbola)

...

$y^2 + y = x^2$

$2y \cdot \frac{dy}{dx} + 1 \cdot \frac{dy}{dx} = 2x$
Factor: $\frac{dy}{dx}(2y + 1) = 2x$
Final: ...
The Logic Check:

In Part I, what is the derivative of the constant "36"? Why does it become 0? Does the size of the constant affect the Speed of the relationship?

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Part III: The Product Trap ($xy$)

Find $\frac{dy}{dx}$ for $xy = 10$.

Use Product Rule: $x \cdot \frac{dy}{dx} + y \cdot (1) = 0$
Solve for $\frac{dy}{dx}$: ...

Part IV: The Challenge (The Ellipse)

The Stretched Circle

Find the slope of the ellipse $x^2 + 4y^2 = 100$.
1. Differentiate...
2. Group...
3. Solve...

...

Part V: Transmission (The Echad Extension)

Teacher Log: The Tangled String

Objective: Explain "Implicit" to a younger student using a knot.

The Activity:
1. Tie two strings together in a messy knot.
2. Pull one string ($x$).
3. Ask: "Did I pull the other string ($y$)? No. But did it move? Yes!"

The Lesson: "In life, things are often knotted together. Even if we can't see the connection, pulling one part moves the other. Math can see the connection even inside the knot."


Response: ___________________________________________________________

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