2c7 bn f(t)sin na,tdt TJo \( sIn na,tdt+ T To TJr(U)sin na,tdt 20 T 20 cos na )+-(cos nO,T-COS n@, no,T no,T 4U7 n为奇数 个(2-2C0Smn) 0 n为偶数1 1 1 1 1 2 2 (cos 1) (cos cos ) 2 2 U T U T n n T n n T n T      = − − + − 4 0 U n   =    n 为奇数 n 为偶数 1 0 2 ( ) sin d T b f t n t t n T =   2 1 1 0 2 2 2 sin d ( ) sin d T T U n t t U n t t T T T = + −     (2 2 cos ) U n n   = −