n元x o sIn 0 0/82,n兀x 元x a U. cos 40 n=1,3,5,7. ni y =∑sin n元x n=135777r2 0 0 0 1 a 0 0 0 0 n=1,3,5,7... sin sin ( ) a cos = 2 4 .....n=1,3,5,7... 4 = sin a a n n n n n y a n x n x U dx A dx a a a n x U A n a U A n U n x e n a          =  − = =    