"Modernization" of an old AIME problem

Find the number of second-degree polynomials f ( x ) f(x) with integer coefficients and integral roots for which f ( 0 ) = 2014 f(0)=2014 .

(Based on 2010 AIME II Problem 10, which I wrote a number of years ago.)


The answer is 55.

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1 solution

Eddie The Head
Apr 13, 2014

Let us consider f ( x ) = a ( x p ) ( x q ) f(x) = a(x-p)(x-q) . hence f ( 0 ) = a p q = 2014 f(0) = apq = 2014 . a p q = 2 19 53 apq = 2*19*53 .

First we consider the cases where a a , p p and q q are all positive. The number of such possibilities is 3 3 = 27 3^{3} = 27 .BUt we must also consider the cases where the values of p p and q q are simply interchanged as they lead to the same equation.There is only one value where p = q = 1 p = q = 1 All others possibilities are double counted.So the number of remaining possibilities 27 1 2 = 13 \frac{27-1}{2}= 13 .

Now we must consider the signs,it is to be noted that whatever we choose the signs of p p and q q ,the sign of a a is automatically determined by the choice to make the the RHS positive.So considering signs There are 2 2 = 4 2*2 = 4 possibilities for each value.But the case in which p = q = 1 |p| = |q|=1 ,there are 3 possibilities as ( p , q ) = ( 1 , 1 ) (p,q) = (1,-1) and ( p , q ) = ( 1 , 1 ) (p,q) = (-1,1) are indistinguishable.

So the total number of possibilities = 13 4 + 3 = 55 13*4+3 = \boxed{55} .

This solution is very similar to the AoPS solution for the AIME II #10 question. :P

Kevin Qian - 7 years, 1 month ago

Use Burnside's Lemma will be shorter (y)

Dani Natanael - 7 years, 1 month ago

Not able to get. Please clearify it Thanks

Archit Agarwal - 6 years, 11 months ago

A beautiful sum.The solution was also nice.

rajdeep brahma - 4 years, 2 months ago

The solution wasn't really clear to me when i read it. I counted each possibility as the number of primes were lesser. Still with the sheer number of possibilities esp with the signs complicated it. Does anyone have a better and easily understandable solution(a simplified and toned down approach)

Sourav Chaudhuri - 7 years, 1 month ago

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