三角函数规律问题谁会求这个式子啊!cosxcos2xcos4xcos8x=?还有一个题 已知2sinx+3siny=a ,2cosx-3cosy=b,求cos(x+y)?

cosxcos2xcos4xcos8x
=sinxcosxcos2xcos4xcos8x/sinx
=(1/2)sin2xcos2xcos4xcos8x/sinx
=(1/4)sin4xcos4xcos8x/sinx
=(1/8)sin8xcos8x/sinx
=1/16 sin16x/sinx
就这样化简,没有别的办法了!!

(sinx*cosxcos2xcos4xcos8x)/sinx
sin2xcos2xcos4xcos8x/2sinx
sin4xcos4xcos8x/4sinx
sin8x*cos8x/8sinx
sin16x/16sinx