Wow this is really hard to read. After staring for some time, I see you're trying to manipulate

And you got

which if you think about it will only be right if n=1; in general it's

Then you have another problem

Question: have you learned factorials?

Lastly you have a question

I don't know how to give a hint, just expand it and you will see that

You can visit the

LaTeX Help subforum to learn about typesetting, and if you double click any rendered LaTeX on the site, it will display the code used to produce it.