To help with a friends homework, I was asked how to solve this equation for $n$: $c(n, n-2) - p(n, 2) = 7 - n$
Having no further information about what c and p are supposed to be (and they don't seem to know either) I assumed they were probably combination and permutation. But when I expanded that out, I was left with a polynomial $n^2 - 3n + 14$ which has complex solutions. Is there something else obvious I'm missing that c and p could be here?