1. The problem statement, all variables and given/known data Fourier series expansion of a signal f(t) is given as f(t) = summation (n = -inf to n = +inf) [3/(4+(3n pi)2) ) * e j pi n t A term in expansion is A0cos(6 pi ) find the value of A0 Repeat above question for A0 sin (6 pi t) 2. Relevant equations Fourier expansion is summation n = -inf to +inf Cn ejwnt where Cn is Integration over T0 x(t) e-jwnt dt 3. The attempt at a solution In book they've said Cn is right. But then they say an is 2 times real part of Cn and have done an = 6/[4 + (18 pi)2 For third part they've put A0sin (6 pi t) = bn sin (n w t) and for n = 6, this is zero. I didn't understand this part. Why did they multiply it by 2 first and then how did it become zero in the second. I understand that sin ( 6 pi) is zero but how can sin ( 6 pi t) be zero? Wouldn't this vary as 't' varies?