化简1/(sin^2 a-cos^2 a)
问题描述：
化简1/(sin^2 a-cos^2 a)
答
sin^2a+cos^2a/sin^2a-cos^2a
答
1/(sin²a-cos²a)
=1/[-(cos²a-sin²a)]
=1/[-cos(2a)]
=-sec(2a)