The function is and , in the interval .

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

.

.

Here the function is differentiable on the interval .

Then .

From the mean value theorem :

Substitute in the above expression.

When then the smallest value of is .

.