化简sin2a(1+tana*tana/2)

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化简sin2a(1+tana*tana/2)

化简sin2a(1+tana*tana/2)
化简sin2a(1+tana*tana/2)

化简sin2a(1+tana*tana/2)
sin2a(1+tana*tana/2)
=2sinacosa[1+(sina/cosa)*(sina/2/cosa/2)]
=2sinacosa+2(sina)^2*[(sina/2)^2/(sina/2*cosa/2)]
=2sinacosa+2(sina)^2[(1-cosa)/sina)]
=2sinacosa+2sina(1-cosa)
=2sina.

令tan (a/2)=t
有cos a=cos^2 (a/2)-sin^2(a/2)=(1-t^2)/(1+t^2)
sin a=2sin (a/2)cos (a/2)=2t/(1+t^2)
tan a=2t/(1-t^2)
sin2a(1+tana*tana/2)
=4t(1-t^2)/(1+t^2)^2*(1+2t^2/(1-t^2))
=4t/(1+t^2)
=2sin a

sin2a(1+tana*tana/2)
=sin2a[(cosA*cosA/2+sinA*sinA/2)/cosA*cosA/2]
=sin2a[cos(A-A/2)/cosA*cosA/2]
=sin2AcosA/2/cosA*cosA/2
=sin2A/cosA
=2sinA