其中 F(z)cos nzdz, T=兀 z sIn n T兀 T F(=f(r) f(x)=0+2(a, cos x+b, sin x) 2 其中 nTt f(x)cos xdx, n70 f(x)sin-xdx( cos sin ) 2 ( ) 1 0 x l n x b l n a a f x n n n  +  = +  = ( )sin . 1 ( )cos , 1    −  −  =  = b F z nzdz a F z nzdz n 其中 n ( )sin . 1 ( )cos , 1   − −  =  = l l n l l n xdx l n f x l b xdx l n f x l 其中 a F(z) f (x) l x z =   =