若tanθ=2,则1\sin^2θ-cos^2θ=

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若tanθ=2,则1\sin^2θ-cos^2θ=若tanθ=2,则1\sin^2θ-cos^2θ=若tanθ=2,则1\sin^2θ-cos^2θ=cos2θ=(1-tan^2θ)/(1+tan^2

若tanθ=2,则1\sin^2θ-cos^2θ=
若tanθ=2,则1\sin^2θ-cos^2θ=

若tanθ=2,则1\sin^2θ-cos^2θ=
cos2θ=(1-tan^2θ)/(1+tan^2θ)
1\sin^2θ-cos^2θ=-1/(cos^2θ-sin^2θ)=-1/cos2θ
=-(1+tan^2θ)/(1-tan^2θ)
=-(1+4)(1-4)=5/3