# Find the derivative of the function using the definition of the derivative. g(x) = 9 − x.

We will use the concept of differentiation by the first principle and find the derivative.

## Answer: The derivative of the function g(x) = 9 - x, using the definition of the derivative, is g'(x) = -1.

Let us see how we will use the concept of differentiation by the first principle and find the derivative.

**Explanation**:

Differentiation by the first principle is stated as,

f^{'}(x) = [f (x + h) - f (x)] / h where h < 0

Hence, let us find derivative for g(x).

g'(x) = [9 - (x + h) - 9 + x] / h

g'(x) = -h / h