证明sin(x+y)sin(x-y)=（sinx）^2-(siny）^2.

证明sin(x+y)sin(x-y)=sinx-siny 一道三角恒等式证明题请证明sin(x+y)sin(x-y)=sin^2(x)-sin^2(y) 已知x+y+z=π,证明sin(x+y)+sin(y+z)+sin(z+x)≥sin2x+sin2y+sin2z 三角不等式证明证明sin(x+y)+sin(y+z)+sin(z+x)>sinx+siny+sinz+sin(x+y+z) 证明sinx+siny+sinz-sin(x+y+z)=4sin((x+y)/2)sin((x+y)/2)sin((x+y)/2) 如果 2sin(x-y)=sin(x+y),证明 tanx= 3 tany 证明sin(x+y)sin(x-y)=（sinx）^2-(siny）^2. 证明 (tanX+tanY)/(tanX-tanY)=(sin(X+Y))/(sin(X-Y))thanks 求证sin²x-sin²y=sin(x+y)sin(x-y) 证明sinx+cos(x+y)siny/cosx-sin(x+y)siny=tan(x+y) 证明tan(x+y)+tan(x-y)=sin2x/cos^2x-sin^2y 证明COS（X+Y）COS（X-Y）=COS^2X-SIN^2Y 证明cos(x+y)cos(x-y)= cos^2(x)-sin^2(y) Mathematica y''+ sin(x) y=x 证明y=sin x 平方 是周期函数 证明y=sinx+sinπx不是周期函数 y=sin²x怎么证明是周期函数? y=sin根号x