已知tanα=2,sin²α-3sinαcosα+1=
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![已知tanα=2,sin²α-3sinαcosα+1=](/uploads/image/z/2738572-52-2.jpg?t=%E5%B7%B2%E7%9F%A5tan%CE%B1%3D2%2Csin%26%23178%3B%CE%B1-3sin%CE%B1cos%CE%B1%2B1%3D)
已知tanα=2,sin²α-3sinαcosα+1=
已知tanα=2,sin²α-3sinαcosα+1=
已知tanα=2,sin²α-3sinαcosα+1=
(sinα)^2-3sinαcosα+1
=[(sinα)^2-3sinαcosα+(sinα)^2+(cosα)^2]/[(sinα)^2+(cosα)^2]
=[2(sinα)^2-3sinαcosα+(cosα)^2]/[(sinα)^2+(cosα)^2] 分子分母同除(cosα)^2
=[2(tanα)^2-3tanα+1]/[(tanα)^2+1]
=(8-6+1)/(4+1)
=3/5