化简sin(x+y)sin(x-y)-cos(x+y)cos(x-y)的结果是?

问题描述:

化简sin(x+y)sin(x-y)-cos(x+y)cos(x-y)的结果是?

原式=-[cos(x+y)cos(x-y)-sin(x+y)sin(x-y)]
=-cos[(x+y)+(x-y)]
=-cos2x

sin(x+y)sin(x-y)-cos(x+y)cos(x-y)
=-cos[(x+y)+(x-y)]
=-cos2x