Primitive of Square of Hyperbolic Secant Function

Theorem

 * $\displaystyle \int \sech^2 x \rd x = \tanh x + C$

where $C$ is an arbitrary constant.

Proof
From Derivative of Hyperbolic Tangent:
 * $\dfrac \d {\d x} \map \tanh x = \map {\sech^2} x$

The result follows from the definition of primitive.