f(tdt (3.1-3a) f(tcosnaotdt (31-3b) 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 