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