求证:sin^2θtanθ+cos^2θcotθ+2sinθcosθ=tanθ+cotθ

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求证:sin^2θtanθ+cos^2θcotθ+2sinθcosθ=tanθ+cotθ
求证:sin^2θtanθ+cos^2θcotθ+2sinθcosθ=tanθ+cotθ

求证:sin^2θtanθ+cos^2θcotθ+2sinθcosθ=tanθ+cotθ
sin^2θtanθ+cos^2θcotθ+2sinθcosθ
=sin³θ/cosθ+cos³θ/sinθ+2sinθcosθ
=sin³θ/cosθ+sinθcosθ+cos³θ/sinθ+sinθcosθ
=(sin³θ+sinθcos²θ)/cosθ+(cos³θ+sin²θcosθ)/sinθ
=sinθ(sin²θ+cos²θ)/cosθ+cosθ(cos²θ+sin²θ)/sinθ
=sinθ/cosθ+cosθ/sinθ
=tanθ+cotθ

左边=sin^3θ/cosθ+cos^3θ/sinθ+2sinθcosθ=(sin^4θ+cos^4θ+2sin^2θcos^2θ)/sinθcosθ=(sin^2θ+cos^2θ)^2/sinθcosθ=1/sinθcosθ=右边
其实就是左边通分算一下就可以了