Primitive of Product of Hyperbolic Secant and Tangent

Theorem

 * $\displaystyle \int \sech x \tanh x \rd x = -\sech x + C$

where $C$ is an arbitrary constant.

Proof
From Derivative of Hyperbolic Secant Function:
 * $\dfrac \d {\d x} \sech x = -\sech x \tanh x$

The result follows from the definition of primitive.