The conditions are  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  .

The functions  and  are continuous on  and differentiable on .

Apply the mean value theorem for the function .

From the mean value theorem :

Substitute  in above expression.

Observe the condition , then .

From equation ,

Then .

.

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