f(tcos notat f(t), tdt+2 f(t)cosnoo tdt f(t)cos(nOot)d(t)+ f(t)cosnoo tdt T f(t)cos noo tdt+2f(t)cosnootdt] 712(oo 类似地 f(t)cos tdt = 2 0 0 ( ) cos 4 T f t n tdt T  f t n tdt T a T n  = 0 ( ) cos 2  −  = + 2 0 0 0 2 0 [ ( )cos ( ) cos ] 2 T T f t n tdt f t n tdt T   [ ( )cos( ) ( ) ( )cos ] 2 2 0 0 0 2  0  = − − − + T T f t n t d t f t n tdt T   [ ( )cos ( ) cos ] 2 2 0 0 2 0  0  = + T T f t n tdt f t n tdt T    = 2 0 0 0 ( ) cos 4 T f t n tdt T 类似地 a 