f(t)at (3.1-3a 2-T2T f(t)cos notdt (3.1-3b f(tsin nootdt n=1, 2. (3. 1-3c(3.1-3a) (3.1-3b) (3.1-3c)  = T f t dt T a ( ) 1 0  = T n f t n tdt T a 0 ( ) cos 2  ( )sin 1,2, 2 = 0 =  f t n tdt n T b T n 