sina+cosa-1)(sina-cosa+1)/sin2a

化简 要过程

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(sina+cosa-1)(sina-cosa+1)/弊伏sin2a
=[sina^2-(cosa-1)^2]/sin2a
=[sina^2-cosa^2+2cosa-1]/租缓携sin2a
=[-2cosa^2+2cosa]/哪消sin2a
=[-2cosa^2+2cosa]/(2sina*cosa)
=[-cosa+1]/sina
=tan(a/2)

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