tan(arctanX+arctanY)=(X+Y)/(1-XY)
问题描述：
tan(arctanX+arctanY)=(X+Y)/(1-XY)
想了很久,没转过来......
还有 sin(2arctanX)=2X/(1+X^2)
答
❶证明：tan(arctanX+arctanY)=(X+Y)/(1-XY) 证明：tan(arctanx+arctany)=(tanarctanx+tanarctany)/[1-(tanarctanx)(tanarctany)]=(x+y)/(1-xy)＝右边.【如果看不明白,可令arctanx=α,arctany=β,那么tanα=ta...