Primitive of x over Cosine of a x

Theorem

 * $\displaystyle \int \frac {x \ \mathrm d x} {\cos a x} = \dfrac 1 {a^2} \left({\frac {\left({a x}\right)^2} 2 + \frac {\left({a x}\right)^4} 8 + \frac {5 \left({a x}\right)^6} {144} + \cdots + \frac {E_n \left({a x}\right)^6} {\left({2 n + 2}\right) \left({2 n}\right)!} + \cdots}\right) + C$

where $E_n$ denotes the $n$th Euler number.

Also see

 * Primitive of $\dfrac x {\sin a x}$