已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a等于多少已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a .
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![已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a等于多少已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a .](/uploads/image/z/1241519-23-9.jpg?t=%E5%B7%B2%E7%9F%A52sina%3D-cosa%2C%E5%88%991%2B2sinacosa%2Fsin%5E2a-cos%5E2a%E7%AD%89%E4%BA%8E%E5%A4%9A%E5%B0%91%E5%B7%B2%E7%9F%A52sina%3D-cosa%2C%E5%88%991%2B2sinacosa%2Fsin%5E2a-cos%5E2a+.)
已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a等于多少已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a .
已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a等于多少
已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a .
已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a等于多少已知2sina=-cosa,则1+2sinacosa/sin^2a-cos^2a .
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
题目中结论中2sinacosa/sin^2a中,化简得2cosa/sina……(1)
其他1-cos^2a化简得 sin^2a ……(2)
又有条件和(1)得-1/4……(3)
又有(2)得sin^2a =(1-cos2a)/2……(4)
又cos2a=cos^2a-sin^2a又从已知条件得(3sin^2a+1)/2……(5)
得到等式(3sin^2a+1...
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题目中结论中2sinacosa/sin^2a中,化简得2cosa/sina……(1)
其他1-cos^2a化简得 sin^2a ……(2)
又有条件和(1)得-1/4……(3)
又有(2)得sin^2a =(1-cos2a)/2……(4)
又cos2a=cos^2a-sin^2a又从已知条件得(3sin^2a+1)/2……(5)
得到等式(3sin^2a+1)/2=sin^2a 得sin^2a =1/7……(6)
由(3)结合(6)得-3/28
其实三角函数并不难,只要认真专研便会柳暗花明,当然,有什么不会可以找我哦!
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