(sin^2a-sinacosa-3cos^2a)/(5sinacosa+sin^2a+1)
=[(sin^2a-sinacosa-3cos^2a)/cos^2a] / [(5sinacosa+sin^2a+1)/cos^2a]
=[tan^2 a - tana -3] / [5tana+tan^2 a +sec^2 a]
=[tan^2 a - tana -3] / [5tana+tan^2 a +(1+tan^2 a)]
=[tan^2 a - tana -3] / [5tana+2tan^2 a +1]
=[-1-根号2] / [5+5根号2]
=-1/5.
2sin^2a-sinacosa+cos^2a
=[(2sin^2a-sinacosa+cos^2a)/cos^2 a]/sec^2 a
=[2tan^2 a - tana +1]/(1+2tan^2 a)
=[5-根号2] / 5
=1-(根号2) / 5
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