其中an=「F(x) cos nzd., F(zsinnzdz. πy-兀 gr ∵Z= F()=f(x) f(x)="+∑( (. cOS x+b, sin- x) 2 n=」 其中an=,f( n几 f∫(x)cos"xdx, b, =f(x)sindo 上或( 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 =   =