u=-(sint+sin 3t +=sin 5t +=sin7t+sin 9t) T 3 5 t 2 u(t)=(sint sin 3t +sin 5t +=sin 7t+...) T 3 5 (一π<t<π,t≠0) 上页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  =