is (at)coskatd (at) 21 sin kot= 0 k Z的展开式为 2 (sin at+ sin 3at sin 5at+... 2 3sin 0 2 1 ( )cos ( ) 2 0 2 0 =  = =          k t k I a i t k td t m k S s i 的展开式为： sin5 ) 5 1 sin3 3 1 (sin 2 2 = + t + t + t + I I i m m S    