u=-(sint +sin 3t+-sin 5t+=sin 7t+sin 9t) 3 u(t)=(sint +sin 3t+-sin 5t+=sin 7t +.. (一π<t<π,t≠0)sin7 ) 7 1 sin5 5 1 sin3 3 1 (sin 4 ( ) + + + +  u t = t t t t (−  t  ,t  0) sin9 ) 9 1 sin7 7 1 sin5 5 1 sin3 3 1 (sin 4 u t + t + t + t + t  =