证由第8页1.6式 1()=1/ f(acos a(t-r)dt do 丌J0 cos a(t-T)=cos at cos Ot+sin at sin at 得1+ f(r)cos a(t-tdt +0 1—元 f(acos at cos atdt+ 1一元 f(osin at sin at dt证 由第8页1.6式 0 cos ( ) 1 f t f ( ) ( ) d d    t    + + −   =     −   cos ( ) cos cos sin sin       t t t − = + 得 cos 1 ( )cos ( ) 1 ( )cos d 1 ( )sin sin d f t d f f t t                + − + − + − − = +   