I am not sure where to start with this problem. . . . . really?
If is a positive integer and ,
prove that: . is a perfect square.
Do you know what those C-expressions mean?
If you do, just do the algebra . . .
. . . etc.
Even after trying to plug the equation I still am unsure how to set up the proof.
C(n, r) = n! / r!(n-r)!
shouldn't the bases of both equations be 2!(n-2)!