Double integral and reversing order

[Nope]

Homework Statement

http://img10.imageshack.us/img10/3390/55486934.jpg

Homework Equations

This is what I was thinking: tan−1(∏x)−tan−1(x)=∫$^{g(x)}_{f(x)}$h(y)dy

The Attempt at a Solution

I don't really understand how to do this question

 

[Dick]

Big hint. You can write the numerator as
$$\int_x^{\pi x} \frac{1}{1+t^2} dt$$
Now follow the rest of the problem suggestion.

 

[Nope]

Thanks for the hint!