已知tanα=-1/2,2sin²α+sinα·cosα-3cos²α的值
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![已知tanα=-1/2,2sin²α+sinα·cosα-3cos²α的值](/uploads/image/z/805691-11-1.jpg?t=%E5%B7%B2%E7%9F%A5tan%CE%B1%3D-1%2F2%2C2sin%26%23178%3B%CE%B1%2Bsin%CE%B1%C2%B7cos%CE%B1-3cos%26%23178%3B%CE%B1%E7%9A%84%E5%80%BC)
已知tanα=-1/2,2sin²α+sinα·cosα-3cos²α的值
已知tanα=-1/2,2sin²α+sinα·cosα-3cos²α的值
已知tanα=-1/2,2sin²α+sinα·cosα-3cos²α的值
sin^2α+2sinαcosα-3cos^2α
=(sin^2α+2sinαcosα-3cos^2a)/(sin^2α+cos^2α)
=(tan^2α+2tanα-3)/(tan^2α+1)
=(1/4-1-3)/(1/4+1)
=-15/5
=-3