Question

find the derivative of :f(x) = sec (u) = 1/cos (u)

Answer 1

$\frac{d}{dx}(\frac{1}{\cos(u)})=\frac{d}{dx}(sec(u))$

Using the rules of the derivate...

Answer:

$\frac{d}{dx}(\frac{1}{\cos(u)})=\sec (u)\cdot\tan (u)$