How to compute $\int_0^2 f(4x)\, dx$ given $\int_0^8 f(x)\, dx=4$ 
Compute $\displaystyle \int_0^2 f(4x)\, dx$ given that $\displaystyle\int_0^8 f(x)\, dx=4$.

At first I thought this was an ‘integrate by recognition’ type of question, I but can’t seem to come up with an answer.
Can someone tell me what sort of method I should use?

Let $u=4x$, then you get $$\int_0^2 f(4x)\, dx= (1/4)\int_0^8 f(u)\, du=1$$
