I am currently learning about hyperbolic functions, and I have been presented with the following:$$\sinh^2 x = \frac{\cosh2 x - 1}{2}$$

This may seem like a simple conversion for some, and my apologies for my ignorance on the topic; however, I do not know where to start with this. If someone could please explain to me the process from "a" to "b" I would be extremely grateful.