已知tanα=2,求下列各式的值

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化简(sin^2a-sinacosa-3cos^2a)/(sinacosa-sin^2a+1)=(cos^2a+cos^2atana)/(2cos^2atan^2a-cos^2atana)=(1+tana)/(2tan^2a-tana)=(1+2)/(2*4-2) =3/2
化简2sin^2a-sinacosa+cos^2a=(2tan^2a-tana+1)/tan^2a+1=7/5