已知2sina=-cosa,则1+2sinacos - 知识问答

已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a等于多少

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已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a
2sina=-cosa
tana=-1/2
(1+2sinacosa)/(sin^2a-cos^2a)
=(sina+cosa)^2/[(sina+cosa)(sina-cosa)]
=(sina+cosa)/(sina-cosa)(分子分母同时除以cosa)
=(tana+1)/(tana-1)
=(-1/2+1)/(-1/2-1)
=-1/3

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