2sin(x+y)*siny+cos(x+2y)可以化简为什么?

问题描述:

2sin(x+y)*siny+cos(x+2y)可以化简为什么?
请尽快回答

2sin(x+y)*siny+cos(x+2y)
=2sin(x+y)*siny+cos[(x+y)+y]
=2sin(x+y)siny+cos(x+y)cosy-sin(x+y)siny
=cos(x+y)cosy+sin(x+y)siny
=cos[(x+y)-y]
=cosx