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(1+tanα+cotα)/(1+tan^2α+tanα)-cotα/(1+tan^2α)=sinα乘cosα

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(1+tanα+cotα)/(1+tan^2α+tanα)-cotα/(1+tan^2α)=sinα乘cosα
麻烦帮忙证明下,
(1+tanα+cotα)/(1+tan^2α+tanα)-cotα/(1+tan^2α)=sinα乘cosα
(1+tanα+cotα)/(1+tan^2α+tanα)-cotα/(1+tan^2α)
=cotα(tanα+tan^2α+1)/(1+tan^2α+tanα)-cotα/(1+tan^2α)
=cotα(1-1/(1+tan^2α))
=cotα*tan^2α/(1+tan^2α)
=tanα/(1+tan^2a)
=sinα/cosα*(1+sin^2α/cos^2α)
=sinαcosα/(cos^2α+sin^2α)
=sinα*cosα=右边