This is a physics problem, but I have some trouble finishing it up. I evaluated an integral, which gave me inv tan of (1-E)tan(theta/2)/(sqrt (1-E^2) evaluated from 0 to 2pi. I changed the limits to 0 to pi, and multipied by 2, because tan x doesn't exist at 2pi. I know that if you take the inverse tangent of a tangent, you'll just get the angle. But because the tan has this ugly coefficient, I can't simply get the angle, right? The answer is pi/2 so I'm inclined to just ignore it...but I know you can't do that...? Thanks a lot!