Hello

Recall what a factorial is. When you take the factorial of a number, you take that number and multiply it by all the numbers preceding it.

For example,

Now to your question.

When you add , we see that this is the same as .

Looking at this closely, we notice that each term has a common factor:

.

So pull out the term , and we are left with .

But , so our answer is

Does this make sense?

--Chris