Question

（COSx）^2--(COSy）^2=(根号3)/2,求SIN(X+Y).SIN(X-Y)=

Answer 1

由条件,有（1 cos2x)/2-(1 cos2y)=a 即cos2x-cos2y=2a sin(x y)*sin(x-y) =(sinx)^2*(cosy)^2-(siny)^2*(cosx)^2 对这个式子中各项降幂,可得 原式=（cos2y-cos2x)/2 =-a