微积分,证明2cos(x+y/2)>cosx+cosy,(x,y)∈(-π/2,π/2)
证明cosx(cosx-cosy)+sinx(sinx-siny)=2sin(x-y)/2
求证cosx-cosy=-2sin (x+y/2)*sin (x-y/2)
已知sinx+siny=(√2)/4,cosx+cosy=1/2,求cos(x-y)的值.
设cosX+cosY=1/2,sinX+sinY =1/4,求cos(X-Y)的值
若sinx-siny=-1/3,cosx-cosy=1/2,则cos(x-y)=?
已知sinx-siny=-1/3,cosx-cosy=1/2,求COS(X—Y)=
sinx+siny=2/5,cosx+cosy=6/5,求cos(2x-2y)
若cosx*cosy+sinx*siny=1/3 ,则cos(2x-2y)=?
已知2cos(2x+y)=cosy,求tan(x+y)tany的值
cosx+cosy=1/2,sinx-siny=1/3,则cos(x+y)=?
已知cosx+cosy=1/2,sinx-siny=1/3,求cos(x+y)
已知x-y=3/π且cosx-cosy=1/3,则cos(x+y)等于多少