求证2(cosθ -sinθ )/1+sinθ +cosθ =tan(π/4-θ /2)-tanθ /2
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求证2(cosθ-sinθ)/1+sinθ+cosθ=tan(π/4-θ/2)-tanθ/2求证2(cosθ-sinθ)/1+sinθ+cosθ=tan(π/4-θ/2)-tanθ/2求证2(cosθ
求证2(cosθ -sinθ )/1+sinθ +cosθ =tan(π/4-θ /2)-tanθ /2
求证2(cosθ -sinθ )/1+sinθ +cosθ =tan(π/4-θ /2)-tanθ /2
求证2(cosθ -sinθ )/1+sinθ +cosθ =tan(π/4-θ /2)-tanθ /2
请参考：
tanθ /2=y
sinθ=2y/(1+y^2)
cosθ=(1-y^2)/(1+y^2)
2(cosθ -sinθ )/(1+sinθ +cosθ)=2(1-y^2-2y)/(1+y^2+2y+1-y^2)=(1-y^2-2y)/(y+1)
=(2-1-y^2-2y)/(y+1) =2/(y+1)-(y+1)
tan(π/4-θ /2)-tanθ /2=[(1-y)/(1+1*y)]-y=(2-1-y)/(1+y) = 2/(y+1)-(y+1)=2(cosθ -sinθ )/(1+sinθ +cosθ).
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