怎样求正切函数的导数

Question

如题所述

Answer 1

(tan x )'=(sin x /cos x)'
=[(sin x)'cos x-sin x(cos x)']/cosx*cos x
=[cos x*cos x-(-sin x*sin x)]/cos x*cos x
=1/cos x*cos x
=1/cos^2x.本回答被网友采纳

Answer 2

cos^2x－sin^2x＝cos2x＝2cos^2x－1=1－2sin^2x≠1