Phase 2 · Math, when you need it · Calculus
Derivatives
The slope at a point: how fast the output changes.
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Why it matters
A derivative answers "if I nudge the input a little, how much does the output change?" Marketers know it as marginal return: the extra conversions from the next $100 of spend. Machine learning uses it for one decision repeated billions of times: for each weight, does nudging it up make the loss go up or down, and by how much? That number tells training which way to move. Everything else in deep learning is bookkeeping around it.
What you'll be able to do
- Explain a derivative as the slope of a function at a point: the rate of change
- Estimate derivatives numerically with a small step
- Read the sign and size of a derivative: uphill, downhill, flat
- Use marginal returns to decide where extra spend stops paying off
Before this lesson
Next in this phase: Derivative rules