Hello,

The question is:

In the binomial expansion of , whereis a constant andkis a positive integer, the coefficient of is equal to the coefficient of . Prove thatn.n= 6k+ 2

I got as far as:

I tried simplifying and got:

I then tried simplifying the factorials, but couldn't see how I was going to end up with the required result.

Some help would be very appreciated.

Thank you.