>>13762531Basically one way to represent sine and cosine is with complex exponentials
sin(x) = (e^ix - e^-ix)/2i
cos(x) = (e^ix + e^-ix)/2
But notice, if x happens to be complex itself, suddenly both of the exponents are real numbers. To handle this condition, mathematicians defined some new functions called the hyperbolic sine, cosine, tangent....etc
Cosh = hyperbolic sine
cosh(x) = (e^x + e^-x)/2
sinh(x) = (e^ - e^-x)/2
Next mathematicians worked out all the various identities you can use with these functions.
For example, cosh^2(x) - sinh^2(x) = 1
https://trigidentities.info/hyperbolic-trig-identities/ 
