Evaluating Integral of a Trigonometric Function: Homework Solution

[ACLerok]

Homework Statement

Evaluate the integral with respect to f of the following function
http://img233.imageshack.us/img233/5303/picture1ub7.png

The Attempt at a Solution

This if for one of my homeworks. I haven't taken a single math course in almost 2 years so I'm kind of rusty. I'm not sure how to evaluate this. I tried moving the 'a' outside the integral but that doesn't help. I believe there is a trig identity I'm supposed to be able to use. Any tips or hints are greatly appreciated.

 

[HallsofIvy]

That is for the form $$\frac{a^2}{a^2+b^2f^2}$$= $$\frac{1}{1+ \left(\frac{bf}{a})^2}$$.
Does it help you to know that the derivative of arctan(x) is $$\frac{1}{x^2+ 1}$$?