Hi guys

I have this problem I'm a little stuck on. It's a 5 part question which leads you through a proof of

In the previous two parts of the question, I was asked to show that

and that

which I did. It's the final part which I'm stuck on. It says the following

"Use your answers to the above two parts to prove that"

I thought it would be simple enough, I proceeded as follows

...and it's here I get stuck. I've looked at it for a while now and can't see how use the above information to derive the required result.

(oh, I can already derive the result using other methods, it's this particular question which is bugging me)

Thanks