# Concept of a derivative

What’s a Derivative?

A more helpful question may be

“What question does a derivative answer?”

Suppose the a variable y depends on x (so that y is a function of x).

Question: If x changes from 102 to 103.4, how much does y change?

Change in y $\approx$ (Derivative) $\times$ (Change in x)

We have

(Change in x)  = $\Delta x$ = 103.4-102 = 1.4.

Therefore

(Change in y) = Derivative  $\times$ 1.4.