# f'(x)?

• October 10th 2012, 03:19 PM
pnfuller
f'(x)?
find f'(x) if it is known that
d/dx [f(2x)]=x2

what does this mean?
• October 10th 2012, 03:28 PM
MarkFL
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:

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