若tanθ=2.则(sin2θ-cos2θ)/1+cos^2θ等于

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若tanθ=2.则(sin2θ-cos2θ)/1+cos^2θ等于
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若tanθ=2.则(sin2θ-cos2θ)/1+cos^2θ等于
若tanθ=2.则(sin2θ-cos2θ)/1+cos^2θ等于

若tanθ=2.则(sin2θ-cos2θ)/1+cos^2θ等于
(sin2θ-cos2θ)/(1+cos^2θ)
=[2sinθcosθ-(cosθ)^2+(sinθ)^2]/[(sinθ)^2+(cosθ)^2+(cosθ)^2]
【分子分母都除以(cosθ)^2】
=[2tanθ+(tanθ)^2-1]/[(tanθ)^2+2]
=(2×2+2^2-1)/(2^2+2)
=7/6