1. The problem statement, all variables and given/known data ∫dt/(t^2 +2tcos a + 1) (Limits of the integral are from 0 to 1) (0<a<π) 2. Relevant equations 3. The attempt at a solution Put t=sin a dt=cosa da ∫dt/(t^2 +2tcos a + 1) = ∫cos a da/(sin^2 a + sin 2a + 1) [ limits of integration changed to 0 to π/2] = ((cosec a)/2) ∫sin 2a da/(sin^2 a + sin 2a + 1) I couldn't figure out what to do next... Please help!!