You need some brackets here I think you mean:

One way is if you know the "Hyperbolic Pythagoras's" theorem:

when it follows at once, but that would be to simple, so we must suppose

that you are expected to expand the hyperbolic funtions in terms of

exponentials. So:

,

and:

,

Then:

,

and:

,

So:

,

and the required result follows on multiplying both sides by

RonL