u=-(sint +sin 3t +=sin 5t +-sin7t+sin 9*) T 3 5 u(t=-(sint + sin 3t +sin 5t+-sin7t+.) T 3 5 (一π<t<π,t≠0sin7 ) 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  =