关于sin,cos,tan,cot,csc,sec
问题描述：
关于sin,cos,tan,cot,csc,sec
coty-tany
----------=csc的二次方y-sec的二次方y
sinycosy
答
(coty-tany)/(sinycosy)
=(cosy/siny-siny/cosy)/sinycosy
=(cos^2y-sin^2y)/sin^2yos^2y
=1/sin^2y-1/cos^2y
=csc^2y-sec^2y