tana=1/2,求值:2sina^2a-sinacosa+cos^2a

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tana=1/2,求值:2sina^2a-sinacosa+cos^2a
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tana=1/2,求值:2sina^2a-sinacosa+cos^2a
tana=1/2,求值:2sina^2a-sinacosa+cos^2a

tana=1/2,求值:2sina^2a-sinacosa+cos^2a
解2sina^2a-sinacosa+cos^2a
=(2sina^2a-sinacosa+cos^2a)/1
=(2sina^2a-sinacosa+cos^2a)/(cos²α+sin²α)
=[(2sina^2a-sinacosa+cos^2a)/cos²α]/[(cos²α+sin²α)/cos²α]
=[(2tan^2a-tana+tan^2a)]/[(1+tan²α]
=[(2(1/2)^2-1/2+(1/2)^2)]/[(1+(1/2)²]
=1/5