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

sinX+sin(X+Y)+sin(X+2Y)/cosX+cos(X+Y)+cos(X+2Y)=sinX+sin(X+2Y)+sin(X+Y)/cosX+cos(X+2Y)+cos(X+Y)=2sin(X+X+2Y)/2cos(X-X-2Y)/2+sin(X+Y)/2cos(X+X+2Y)/2cos(X-X-2Y)/2+cos(X+Y)=2sin(X+Y)cosY+sin(X+Y)/2cos(X+...看起来有点复杂，请问能变得简单点吗？这是必须的步骤，没法再简单点了