Problem

Problem

If f′(1)=1f'(1) = 1 and ddx(f(2x))=f′(x)\frac{d}{dx}(f(2x)) = f'(x) , ∀x>0\forall x > 0 . If f′(x)f'(x) is differentiable, then there exists a number c∈(2,4)c \in (2, 4) such that f′′(c)f''(c) is equal to a. −1/4-1/4 b. −1/8-1/8 c. 1/41/4 d. 1/81/8

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