Inverse Hyperbolic Tangent is Odd Function/Proof 2
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Theorem
- $\map {\tanh^{-1} } {-x} = -\tanh^{-1} x$
Proof
\(\ds \map {\tanh^{-1} } {-x}\) | \(=\) | \(\ds \frac 1 2 \map \ln {\frac {1 + \paren {-x} } {1 - \paren {-x} } }\) | Definition 2 of Inverse Hyperbolic Tangent | |||||||||||
\(\ds \) | \(=\) | \(\ds \frac 1 2 \map \ln {\frac {1 - x} {1 + x} }\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds \frac 1 2 \paren {\map \ln {1 - x} - \map \ln {1 + x} }\) | Difference of Logarithms | |||||||||||
\(\ds \) | \(=\) | \(\ds -\frac 1 2 \paren {\map \ln {1 + x} - \map \ln {1 - x} }\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds -\frac 1 2 \map \ln {\frac {1 + x} {1 - x} }\) | Difference of Logarithms | |||||||||||
\(\ds \) | \(=\) | \(\ds -\tanh^{-1} x\) | Definition 2 of Inverse Hyperbolic Tangent |
$\blacksquare$