Inverse Hyperbolic Cotangent of Imaginary Number
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Theorem
- $\map {\coth^{-1} } {i x} = i \cot^{-1} x$
Proof
\(\ds y\) | \(=\) | \(\ds \map {\coth^{-1} } {i x}\) | ||||||||||||
\(\ds \leadsto \ \ \) | \(\ds \coth y\) | \(=\) | \(\ds i x\) | Definition of Inverse Hyperbolic Cotangent | ||||||||||
\(\ds \leadsto \ \ \) | \(\ds i \coth y\) | \(=\) | \(\ds - x\) | $i^2 = -1$ | ||||||||||
\(\ds \leadsto \ \ \) | \(\ds \map \cot {i y}\) | \(=\) | \(\ds x\) | Hyperbolic Cotangent in terms of Cotangent | ||||||||||
\(\ds \leadsto \ \ \) | \(\ds i y\) | \(=\) | \(\ds \cot^{-1} x\) | Definition of Inverse Cotangent | ||||||||||
\(\ds \leadsto \ \ \) | \(\ds y\) | \(=\) | \(\ds -i \cot^{-1} x\) | multiplying both sides by $-i$ |
$\blacksquare$
Sources
- 1968: Murray R. Spiegel: Mathematical Handbook of Formulas and Tables ... (previous) ... (next): $\S 8$: Hyperbolic Functions: $8.99$: Relationship between Inverse Hyperbolic and Inverse Trigonometric Functions