1. The problem statement, all variables and given/known data The problem is f(x) = sin2πx - (1/πsquare)*sinπx and its given Bn sin (nπx) = f(x) Question is find Bn. 2. Relevant equations Bn = 2/L ∫ (sin2πx - (1/πsquare)*sinπx) * sin(nπx/L) where L is 1 3. The attempt at a solution I did ∫ sin2πx * sin (nπx) - (1/πsquare)*sin square πx then I tried changing it to cos but it doesn't make sense, for the first term ∫sin2πx * sin (nπx) ∫sin2πx * sin (nπx) = -1/2 ∫cos(2π+nπ)-cos(2π-nπ) But how do i actually integrate the above with the n in it i am so confused.....I know cosnπ = (-1)^n but I can only use that after final integration and even if I finally somehow manage to integrate it, it will be changed to sinnπ. Please can anyone help!!! . Is there any simple way to do this?