2E 2E m(1-cosn丌)=-m[1-(-1)" n 4E ,n=2k-1,k=1 (2k-1)兀 n=2k,k=1,2, 所求函数的傅氏展开式为 ∑ 4E sin(2n-lt m(2n-1)兀 (-∞<t<+o;t≠0,土π,±2T,…)(1 cos ) 2 −   = n n Em [1 ( 1) ] 2 m n n E − −  =     = = = − = = −    0, 2 , 1,2, , 2 1, 1,2, (2 1) 4 n k k n k k k Em 所求函数的傅氏展开式为   = − −  = 1 sin(2 1) (2 1) 4 ( ) n m n t n E u t (−  t  +; t  0,  ,  2, )