(1-tan^4θ)cos^2θ+tan^2θ
问题描述：
(1-tan^4θ)cos^2θ+tan^2θ
答
因为
(1-tan^4x)cos^2x+tan^2x
=(1+tan^2x)(1-tan^2x)cos^2x+tan^2x
=(1-tan^2x)[(cos^2x+sin^2x)/cos^2x]cos^2x+tan^2x
=1-tan^2x+tan^2x
=1