「 sinmesinnxdx={0,m≠n, =n ∫0,m≠n cos r cos nra 兀,m=n sin mx cos ndx=0.(其中m,n=1,2,…), , 0, sin sin     =  =   − m n m n mx nxdx , , 0, cos cos     =  =   − m n m n mx nxdx sin cos = 0.   − mx nxdx (其中m,n = 1,2, )