The function is , .

Mean value theorem :

Let be a function that satisfies the following three hypotheses.

1. is continuous on .

2. is differentiable on .

Then there is a number  in such that

.

The function is .

The function is continuous on the interval .

Differentiate on each side with respect to .

.

The function is differentiable on the interval .

Then .

From the mean value theorem :

.

Substitute in .

is not in the interval , hence it is not considered.

Therefore .

.