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Algebra Difficulty 4.7 AIME Find the answer

Find all the integer solutions of the equation

9x2y2+9xy2+6x2y+18xy+x2+2y2+5x+7y+6=0 9 x^{2} y^{2}+9 x y^{2}+6 x^{2} y+18 x y+x^{2}+2 y^{2}+5 x+7 y+6=0

A number or a short expression. Spacing and $ signs are ignored.

Solution

The equation is equivalent to the following one

(9y2+6y+1)x2+(9y2+18y+5)x+2y2+7y+6=0(3y+1)2(x2+x)+4(3y+1)x+2y2+7y+6=0 \begin{aligned} & \left(9 y^{2}+6 y+1\right) x^{2}+\left(9 y^{2}+18 y+5\right) x+2 y^{2}+7 y+6=0 \\ & \Leftrightarrow(3 y+1)^{2}\left(x^{2}+x\right)+4(3 y+1) x+2 y^{2}+7 y+6=0 \end{aligned}

Therefore 3y+13 y+1 must divide 2y2+7y+62 y^{2}+7 y+6 and so it must also divide

9(2y2+7y+6)=18y2+63y+54=2(3y+1)2+17(3y+1)+35 9\left(2 y^{2}+7 y+6\right)=18 y^{2}+63 y+54=2(3 y+1)^{2}+17(3 y+1)+35

from which it follows that it must divide 35 as well. Since 3y+1Z3 y+1 \in \mathbb{Z} we conclude that y{0,2,2,12}y \in\{0,-2,2,-12\} and it is easy now to get all the solutions (2,0),(3,0),(0,2),(1,2)(-2,0),(-3,0),(0,-2),(-1,2).

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.