Primitive of Reciprocal of Hyperbolic Cosine of a x plus 1

Theorem

 * $\ds \int \frac {\d x} {\cosh a x + 1} = \frac 1 a \tanh \frac {a x} 2 + C$

Also see

 * Primitive of $\dfrac 1 {\cosh a x - 1}$