sin(x-27°)cos(18°-x)-sin(60°-x)sin(x-18°)为啥答案给的可以化简为sin(x+27°)cos(18°-x)+cos(90°-63°+x)sin(18°-x)

问题描述:

sin(x-27°)cos(18°-x)-sin(60°-x)sin(x-18°)
为啥答案给的可以化简为sin(x+27°)cos(18°-x)+cos(90°-63°+x)sin(18°-x)