Find the number of second-degree polynomials with integer coefficients and integral roots for which .
(Based on 2010 AIME II Problem 10, which I wrote a number of years ago.)
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Let us consider f ( x ) = a ( x − p ) ( x − q ) . hence f ( 0 ) = a p q = 2 0 1 4 . a p q = 2 ∗ 1 9 ∗ 5 3 .
First we consider the cases where a , p and q are all positive. The number of such possibilities is 3 3 = 2 7 .BUt we must also consider the cases where the values of p and q are simply interchanged as they lead to the same equation.There is only one value where p = q = 1 All others possibilities are double counted.So the number of remaining possibilities 2 2 7 − 1 = 1 3 .
Now we must consider the signs,it is to be noted that whatever we choose the signs of p and q ,the sign of a is automatically determined by the choice to make the the RHS positive.So considering signs There are 2 ∗ 2 = 4 possibilities for each value.But the case in which ∣ p ∣ = ∣ q ∣ = 1 ,there are 3 possibilities as ( p , q ) = ( 1 , − 1 ) and ( p , q ) = ( − 1 , 1 ) are indistinguishable.
So the total number of possibilities = 1 3 ∗ 4 + 3 = 5 5 .