若cos(x+y)cosy+sin(x+y)siny=0,则cosx=

若cos(x+y)cosy+sin(x+y)siny=0,则cosx= 若cosx*cosy+sinx*siny=1/3 ,则cos(2x-2y)=? 已知sinx+siny=1/3,cosx-cosy=1/5,求cos(x+y),sin(x-y). 已知sinα+sinX+sinY=0,cosα+cosX+cosY=0,则cos（X-Y） 求思路过程.跪谢 cosx+cosy=1/2,sinx-siny=1/3,则cos(x+y)=? sinx+siny+sinz=0;cosx+cosy+cosz=0;求cos(x-y) 证明cosx(cosx-cosy)+sinx(sinx-siny)=2sin(x-y)/2 已知sinx+siny+sinz=0,cosx+cosy+cosz=0 则cos（x-y）=______ 要详解 若sinx-siny=-1/3,cosx-cosy=1/2,则cos（x-y）=? 已知cos(x+y)cosy+sin(x+y)siny=4/5,求tanx的值 sinX+sinY=1 cosX+cosY=0 求cos(2X)+cos(2Y)的值 已知cosx+cosy=1/2,sinx-siny=1/3,求cos(x+y)