(Note: The ? is where I have to fill in something)
Prove:
$ \begin{align} \sinh2x & = 2\sinh x\cosh x\\ \sinh2x & = \sinh (x + ?)\\ & = \sinh x(?) + \cosh x \sinh x\\ & =\space?\\ \end{align} $
I know that there is a way of proving it by using the basic definitions of $\cosh$ and $\sinh$, but that is not what the question is asking.