Volume 3: The Calculus of Life

Workbook 21.1: The Tangent Line

Directives for the Tracer:

1. Identify the Touch: A Tangent Line touches the curve at one local point.
2. Identify the Direction: The line must go the same way the curve is going at that moment.
3. Estimate the Slope: Use Rise/Run on the grid to estimate how steep the tangent is.
4. The Sign: Up = Positive. Down = Negative. Flat = Zero.

Part I: Visualizing the Tangent

For each description, sketch the curve and the tangent line at the specified point.

The Peak: Draw a hill (parabola facing down). Draw the tangent line at the very top.

[Drawing Area]
Is the slope Positive, Negative, or Zero?

The Climb: Draw a curve that is going up steeply. Draw the tangent.

[Drawing Area]
Is the slope steep (large number) or shallow (small number)?

Part II: Secant vs. Tangent

Using the function $y = x^2$. We want to find the slope at $x=2$.

The Wide Secant: Find the slope between $x=2$ and $x=3$.

$y_1 = 2^2 = 4$. $y_2 = 3^2 = 9$.
Slope = $(9-4) / (3-2) = ...$

The Narrow Secant: Find the slope between $x=2$ and $x=2.1$.

$y_1 = 4$. $y_2 = 2.1^2 = 4.41$.
Slope = $(4.41 - 4) / (2.1 - 2) = ...$

The Prediction: Based on the Narrow Secant, what whole number do you think the slope is approaching?

...
The Logic Check:

Why can't we just use the slope formula on the point $(2, 4)$ by itself? What happens if we try $\frac{4-4}{2-2}$?

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Part III: The Tangent of the Circle

The Radius Rule: Draw a circle. Draw a Radius from the center to the edge. Draw a Tangent line at that edge point.
What is the angle between the Radius and the Tangent?

[Drawing Area]
Is it 45 degrees? 90 degrees? 180 degrees?

Part IV: The Challenge (The Zoom)

Local Linearity Test

Take the function $y = \sin(x)$ (a wave).
If you zoom in very close to $x=0$, the curve looks like a straight line.
Task: Calculate $\sin(0.1)$ and $\sin(0.01)$ on your calculator. Compare them to $x$ (0.1 and 0.01).
Does $\sin(x) \approx x$ when $x$ is small?

$\sin(0.1) = ...$
$\sin(0.01) = ...$
Conclusion: The tangent line is $y = x$.

Part V: Transmission (The Echad Extension)

Teacher Log: The Straight Path

Objective: Teach a younger student that "Straight" is hidden inside "Curved."

The Activity:
1. Draw a circle on the ground with chalk.
2. Have them walk the circle.
3. Tell them to "Freeze."
4. Lay a stick down next to their feet pointing the way they were facing. The stick is straight.

The Lesson: "Even when you walk in circles, each step is straight. God guides our steps (straight) to make our path (curve)."


Response: ___________________________________________________________

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