证明：左边=(2sinα-2sinαcosα)/(2sinα+2sinαcosα)=(1-cosα)/(1+cosα)
=2sin²(α/2)/2cos²(α/2)=tan²(α/2)=右边(那个是α吧)可以帮我回答一下tan(π/4+α）-cot（π/4+α)=2tan2α证明：tan(π/4-α)=cot(π/4+α)左边=(1+tanα)/(1-tanα)-(1-tanα)/(1+tanα)=4tanα/(1-tan²α)(通分)右边=4tanα/(1-tan²α)=左边∴tan(π/4+α）-cot（π/4+α)=2tan2α