Hello! A book on calculus was introducing hyperbolic functions and pointed out that the identities such as cosh x and sinh x, etc. for hyperbolic functions were analogous to cos x and sin x for circular functions. I tried finding some internet sources explaining why this is so, but they tend to be overly complicated or unsatisfactory. Could someone point me in the direction of any recommended sources; or, perhaps, offer a brief explanation (presumably the explanation is not so brief!…) Thanks in advance.