tanθ=4/3,求cos2θ=
问题描述：
tanθ=4/3,求cos2θ=
答
cos2θ=(cos²θ-sin²θ)/1=(cos²θ-sin²θ)/(sin²θ+cos²θ)=(1-tan²θ)/(tan²θ+1)=-7/25
tanθ=4/3,求cos2θ=
cos2θ=(cos²θ-sin²θ)/1=(cos²θ-sin²θ)/(sin²θ+cos²θ)=(1-tan²θ)/(tan²θ+1)=-7/25