化简cos(x+y)sinx-sin(x+y)cosx

化简sin(x+y)sinx+cos(x+y)cosx等于? 化简sin(x+y)sinx+cos(x+y)cosx 化简cos(x+y)sinx-sin(x+y)cosx sinx*sin(x+y)+cosx*cos(x+y)等于? cos（x+y）sinx-sin（x+y）cosx y=cosX,y= - cos(-X) 与y=sinX,y= - sin(-X) 为什么? 为什么y=sinx,y=-sin(-x)=sinx,y=cosx,y=-cos(-x)=-cosx 请问怎么证明sinX+sin(X+Y)+sin(X+2Y)/cosX+cos(X+Y)+cos(X+2Y)=tan(X+ y=sin²X+2sinX*cosX+3COS²X的最大值是? y=sin^2x+2sinx*cosx+3cos^2x y=sin X cos X +sinX +cosX如何化简? 已知sinx+siny=1/3,cosx-cosy=1/5,求cos(x+y),sin(x-y).