Differentiability: Mean Value Theorem - Maximum

Calculus Level 2

f ( x ) f(x) is a function that is continuous and differentiable in the domain [ 7 , 15 ] [7,15] . If f ( 7 ) = 21 f(7) = 21 and f ( x ) 14 f'(x) \leq 14 for all 7 x 15 7\leq x \leq 15 , what is the maximum possible value of f ( 15 ) ? f(15)?


The answer is 133.

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1 solution

Brilliant Mathematics Staff
Aug 1, 2020

Using mean value theorem, we have 14 f ( x ) = f ( 15 ) f ( 7 ) 15 7 = f ( 15 ) 21 8 . 14 \geq f(x) = \frac{f(15) - f(7)}{15 - 7} = \frac{f(15) - 21}{8} .

Simplifying this gives f ( 15 ) 133 . f(15) \leq \boxed{133}.

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