证明.(sinx+siny)/cosx-cosy=ctg(y-x)/2
证明cosx(cosx-cosy)+sinx(sinx-siny)=2sin(x-y)/2
证明sin(x+y)=sinx*cosy+cosx*siny的过程
sinx+siny=2/5,cosx+cosy=6/5,求cos(2x-2y)
若cosx*cosy+sinx*siny=1/3 ,则cos(2x-2y)=?
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)
sinx+siny=-1/3 cosx+cosy=1/2,求sin(x+y)的值.
已知sinx-siny=1/2,cosx-cosy=1/2,x、y均为锐角,求sin(x-y)
sinx+siny=√2/2 cosx+cosy=√6/2 求sin(x+y)求解答.
已知sinx+siny=(√2)/4,cosx+cosy=1/2,求cos(x-y)的值.
sinX+sinY=1 cosX+cosY=0 求cos(2X)+cos(2Y)的值
sinx+siny=1/2,cosx+cosy=(根号3)/3,求sin[(x-y)/2]