## Calculus: Early Transcendentals 8th Edition

$y'=tan(x)$
Start with the function: $y=ln(sec(x))$. Use chain rule to differentiate: $y'=\frac{1}{sec(x)}*\frac{d}{x}(sec(x))$. Differentiate $sec(x)$ and plug in: $y' = \frac{sex(x)tan(x)}{sec(x)}$. Simplify to arrive at the answer: $y'=tan(x)$.