Relationship between cosh and cos
From specialfunctionswiki
Theorem
The following formula holds: $$\cosh(z)=\cos(iz),$$ where $\cosh$ is the hyperbolic cosine and $\cos$ is the cosine.
Proof
References
- 1964: Milton Abramowitz and Irene A. Stegun: Handbook of mathematical functions ... (previous) ... (next): $4.5.8$