# What is the derivative of ln( secx+tanx)?

$f ' \left(x\right) = \sec x$
$f ' \left(x\right) = \frac{1}{\sec x + \tan x} \cdot \left(\sec x \tan x + {\sec}^{2} x\right)$
$f ' \left(x\right) = \frac{1}{\sec x + \tan x} \cdot \sec x \left(\tan x + \sec x\right)$
$f ' \left(x\right) = \sec x$