sin(x+y)-sinx=2siny/2·cos(x+y/2)怎么来的

证明sin(x+y)sin(x-y)=sinx-siny 证明 [sin(2x+y)/sinx]-2cos(x+y)=siny/sinx 求证sin（2x+y)/sinx-2cos(x+y)=siny/sinx 求证：sin(2x+y)/sinx-2cos(x+y)=siny/sinx 证明sin(x+y)sin(x-y)=（sinx）^2-(siny）^2. 证明sinx+cos(x+y)siny/cosx-sin(x+y)siny=tan(x+y) 证明cosx(cosx-cosy)+sinx(sinx-siny)=2sin(x-y)/2 为什么sinx*cosy-cosx*siny=sin(x-y) 求函数z=sinx+siny+sin(x+y)(0 存在sin( x -y) = sinX-sinY吗 请问,如何证明sinx+siny=2*sin(x+y/2)*cos(x-y/2) 为什么sin（x+y) - sinx = 2cos(x+y/2)siny/2 求推导sinx-siny=2cos（(x+y)/2)sin((x-y)/2) 求证sinx+siny=2sin(x+y)/2*cos(x-y)/2 求证:sinx+siny=2sin(x+y)/2cos(x-y)/2 求证|sinx-siny|=|2sin[(x-y)/2]cos[(x+y)/2]| sin(x+y)-sinx=2siny/2·cos(x+y/2)怎么来的 arcsin(sinx+siny)+arc(sinx-siny)=kπ/2,K为奇数,求sin^2x+sin^2y的值