化简sin(x-25°)sin(65°-x)+cos(x-25°)cos(65°-x)的结果为

问题描述:

化简sin(x-25°)sin(65°-x)+cos(x-25°)cos(65°-x)的结果为

原式= cos[(x-25)-(65-x)]
=cos(2x-90)
=sin2x