Question

integral de du/cos²u

Answer 1

$\displaystyle\int \dfrac{du}{\cos^2 u}\\\\\\ =\int \left(\dfrac{1}{\cos u} \right )^2du\\\\\\ =\int (\sec u)^2\,du\\\\\\ =\int \sec^2 u\,du\\\\\\ =\mathrm{tg\,}u+C$