Pythagorean identity for tanh and sech
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Theorem
The following formula holds: $$\mathrm{tanh}^2(z)+\mathrm{sech}^2(z)=1,$$ where $\mathrm{tanh}$ denotes the hyperbolic tangent and $\mathrm{sech}$ denotes the hyperbolic secant.
Proof
References
- 1964: Milton Abramowitz and Irene A. Stegun: Handbook of mathematical functions ... (previous) ... (next): $4.5.17$
