已知tana=-1/2,则2sinacosa/sin^2a-cos^2a的值是
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![已知tana=-1/2,则2sinacosa/sin^2a-cos^2a的值是](/uploads/image/z/1116871-7-1.jpg?t=%E5%B7%B2%E7%9F%A5tana%3D-1%2F2%2C%E5%88%992sinacosa%2Fsin%5E2a-cos%5E2a%E7%9A%84%E5%80%BC%E6%98%AF)
已知tana=-1/2,则2sinacosa/sin^2a-cos^2a的值是
已知tana=-1/2,则2sinacosa/sin^2a-cos^2a的值是
已知tana=-1/2,则2sinacosa/sin^2a-cos^2a的值是
2sinacosa/(sin²a-cos²a)=sin2a/(﹣cos2a)=﹣tan2a=﹣2tana/(1-tan²a)
=﹣2×(﹣1/2)/[1-(﹣1/2)²]=1/(3/4)=4/3