已知tana=3.求sin2a+sinacosa+2cos2a
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![已知tana=3.求sin2a+sinacosa+2cos2a](/uploads/image/z/10146256-16-6.jpg?t=%E5%B7%B2%E7%9F%A5tana%3D3.%E6%B1%82sin2a%2Bsinacosa%2B2cos2a)
已知tana=3.求sin2a+sinacosa+2cos2a
已知tana=3.求sin2a+sinacosa+2cos2a
已知tana=3.求sin2a+sinacosa+2cos2a
(sin2a+sinacosa+2cos2a)
=(sin2a+sinacosa+2cos2a)/1
=(2sinacosa+sinacosa+2cos^2a-2sin^2a)/(sin^2a+cos^2a)
=(3sinacosa+2cos^2a-2sin^2a)/(sin^2a+cos^2a) (上下同除cos^2a)
=(3tana+2-2tan^2a)/(tan^2a+1)
=(9+2-18)/(9+1)
=-4/5