## Calculus, 10th Edition (Anton)

$y'= \dfrac{\sec ^2 x}{\tan x}$
In order to derivate this function you have to apply the chain rule Let's make an «u» substitution to make it easier $f(u) = \ln(u)$ $u' = \tan x$ Derivate the function: $f'(u) = \dfrac{u'}{u}$ Now let's find u' $u' = \sec ^2 x$ Then undo the substitution, simplify and get the answer: $f'(x) = \dfrac{\sec ^2 x}{\tan x}$