# Math Help - f'(x)?

1. ## f'(x)?

find f'(x) if it is known that
d/dx [f(2x)]=x2

what does this mean?

2. ## Re: f'(x)?

We are told:

$\frac{d}{dx}(f(2x))=x^2$

Using the chain rule, we find:

$2f'(2x)=x^2$

$f'(2x)=\frac{x^2}{2}=\frac{4x^2}{8}=\frac{(2x)^2}{ 8}$ and so we must have:

$f'(x)=\frac{x^2}{8}$