证明tan^θ-sin^2θ=tan^2θsin^2θ证明(1)tan^θ-sin^2θ=tan^2θsin^2θ(2)sin^4x+cos^4x=1-2sin^2cos^2x(31-tan^2x/1+tan^2x=cos^2x-sin^2x

问题描述:

证明tan^θ-sin^2θ=tan^2θsin^2θ
证明(1)tan^θ-sin^2θ=tan^2θsin^2θ
(2)sin^4x+cos^4x=1-2sin^2cos^2x
(31-tan^2x/1+tan^2x=cos^2x-sin^2x

(1)tan^2θ-sin^2θ=sin^2θ/cos^2θ-sin^2θ=(sin^2θ-sin^2cos^2θ)/cos^2θ=sin^2θ(1-cos^2θ)/cos^2θ=sin^4θ/cos^2θ=(sin^2θ/cos^2θ)sin^2θ=tan^2θsin^2θ(2)sin^4x+cos^4x=(sin^2x+cos^2x)^2-2sin^...