证明：sin^(x+y)≤(x+y)^2 D为任意有界闭区域sin^2(x+y)≤(x+y)^2

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) 证明sin(x+y)sin(x-y)=sinx-siny 证明：sin^(x+y)≤(x+y)^2 D为任意有界闭区域sin^2(x+y)≤(x+y)^2 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) 证明sinx+siny+sinz-sin(x+y+z)=4sin((x+y)/2)sin((x+y)/2)sin((x+y)/2) 证明sin(x+y)sin(x-y)=（sinx）^2-(siny）^2. 如果 2sin(x-y)=sin(x+y),证明 tanx= 3 tany 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) 请问怎么证明sinX+sin(X+Y)+sin(X+2Y)/cosX+cos(X+Y)+cos(X+2Y)=tan(X+Y), 证明cosx-cos(x+2y)/2siny= sin(x+y)证明cosX-cos(x+2y)/2siny= sin(x+y) 请问,如何证明sinx+siny=2*sin(x+y/2)*cos(x-y/2) 证明 [sin(2x+y)/sinx]-2cos(x+y)=siny/sinx 证明sin2x+sin2y=2sin(x+y)cos(x-y)怎么做 证明cos²x-cos²y=sin²(x-y)-2sinxcosysin(x-y).万分感激! 证明不等式|X|-|Y|≤|X-Y| 已知x+y+z=π,证明sin(x+y)+sin(y+z)+sin(z+x)≥sin2x+sin2y+sin2z