Primitive of Square of Hyperbolic Tangent Function

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Theorem

$\ds \int \tanh^2 x \rd x = x - \tanh x + C$

where $C$ is an arbitrary constant.


Proof

\(\ds \int \tanh^2 x \rd x\) \(=\) \(\ds \int \paren {1 - \sech^2 x} \rd x\) Sum of Squares of Hyperbolic Secant and Tangent
\(\ds \) \(=\) \(\ds \int 1 \rd x - \int \sech^2 x \rd x\) Linear Combination of Primitives
\(\ds \) \(=\) \(\ds \int 1 \rd x - \tanh x + C\) Primitive of Square of Hyperbolic Secant Function
\(\ds \) \(=\) \(\ds x - \tanh x + C\) Primitive of Constant

$\blacksquare$


Sources