Doubling identity for cosh (3)
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Theorem
The following formula holds: $$\cosh(2z)=\cosh^2(z)+\sinh^2(z),$$ where $\cosh$ denotes hyperbolic cosine and $\sinh$ denotes hyperbolic sine.
Proof
References
- 1964: Milton Abramowitz and Irene A. Stegun: Handbook of mathematical functions ... (previous) ... (next): $4.5.32$
