Question

$\int\limits^ \frac{ \pi }{3} _0 \frac{dx}{cos^2x}$

Answer 1

$\displaymath \int \limits_{0}^{\pi/3} \dfrac{\mathrm dx}{\cos^2 x} = \mathrm{tg} \: x \Bigg| \limits_{0}^{\pi/3} = \sqrt{3}$