Chapter 02

DERIVATIVES

Limits taught us how to zoom in infinitely close. Now, we use that power to measure Instantaneous Change.

Every point on a curve has a secret direction. The Derivative reveals it.

Concept Zero: The Instantaneous Slope
Tangent Surfer
Current Position
x : 2.00y : 1.71
Slope (f') : 0.384
Move Cursor to Surf

Don't Memorize. Visualize.

The red line is the Tangent Line. Its slope tells you exactly how fast the function is growing or shrinking at that specific moment.

Notice how the slope is 0 at the peaks and valleys? That's not a coincidence. That's optimization.

INTERACTIVE PREVIEW

Notation Decoder

f'(x)
Lagrange's Notation

"F prime of x". Best for general functions. Shows that the derivative is itself a function.

dy/dx
Leibniz's Notation

"The change in y divided by the change in x". Best for remembering that slope is a ratio.

Dx[y]
Euler's Notation

"The derivative operator". Best for thinking of differentiation as an action you perform.