sin^2 a/sec^2-1 +cos^2 a/csc^2-1+cos^acsc^a
问题描述：
sin^2 a/sec^2-1 +cos^2 a/csc^2-1+cos^acsc^a
答
sin^2/tan^2+cos^2/cot^2+cos^a/sin^a
=cos^2+cos^2*tan^2+1/tan^2
=cos^2+sin^2+cot^2
=1+cot^2