请问怎么证明sinX+sin(X+Y)+sin(X+2Y)/cosX+cos(X+Y)+cos(X+2Y)=tan(X+Y),

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sin(x+y)sin(x-y)=sinx-siny 请问,如何证明sinx+siny=2*sin(x+y/2)*cos(x-y/2) 请问怎么证明cosnx*sinx+sinnx*cosx=sin(n+1)*x? 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y=sinx+sinπx不是周期函数 证明 [sin(2x+y)/sinx]-2cos(x+y)=siny/sinx 证明sin(x+y)sin(x-y)=（sinx）^2-(siny）^2. Δy=sin(x+Δx)-sinx=2cos(x+Δx/2)sin Δx/2怎么证明这个等式成立 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 y=[√（1+sin^2x)+sinx+1]/[√（1+sin^2x)+sinx-1]判断并证明奇偶性 证明sinx+siny+sinz-sin(x+y+z)=4sin((x+y)/2)sin((x+y)/2)sin((x+y)/2) y=sinx+sin|x| 怎么证明(1/2)sinx=sin(x/2)cos(x/2)怎么证明(1/2)sinx=sin(x/2)cos(x/2) 1-cosX/sinX=tan(X/2) 请问怎么证明, z=sinx/sin(x+y)偏导怎么求?如题,sinx/sin(x+y)偏导 存在x,使得sin(x-y)=sinx-xiny,求证明