sin(x-y)sin(x+y)-cos(x-y)cos(x+y)
问题描述:
sin(x-y)sin(x+y)-cos(x-y)cos(x+y)
答
sin(x-y)sin(x+y)-cos(x-y)cos(x+y)
=-cos[(x-y)+(x+y)]
=-cos2x