1996 AIME Problems/Problem 3

Revision as of 15:04, 24 September 2007 by 1=2 (talk | contribs) (Solution)

Problem

Find the smallest positive integer $n$ for which the expansion of $(xy-3x+7y-21)^n$, after like terms have been collected, has at least 1996 terms.

Solution

We can factor that into

$(y-3)^n(x+7)^n$

Now that has at least 1996 terms. Therefore, each of the two factors has at least $\dfrac{1996}{2}=998$ terms. When y-3 has x terms, n=x-1. Therefore, n=998-1=997

See also