Difference between revisions of "1996 AIME Problems/Problem 3"

(Problem)
(Solution)
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== Solution ==
 
== Solution ==
 +
We can factor that into
 +
 +
<math>(y-3)^n(x+7)^n</math>
 +
 +
Now that has at least 1996 terms. Therefore, each of the two factors has at least <math>\dfrac{1996}{2}=998</math> terms. When y-3 has x terms, n=x-1. Therefore, n=998-1=997
  
 
== See also ==
 
== See also ==
 
* [[1996 AIME Problems]]
 
* [[1996 AIME Problems]]

Revision as of 15:04, 24 September 2007

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