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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?

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    Then your friend should either be asking his/her teacher, or consulting his/her textbook to know the meaning of `c` and `p`...2011-11-22
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    I also get that polynomial. Hmm, you might as well ask more details from your friend.2011-11-22
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    I get the same; the equation has no solutions if $c$ and $p$ are indeed combinations and permutations.2011-11-22

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