Integer Odyssey


Find all the integer solutions to the equation $x^2-12y+4=0.$


Source: BdMO 2023 National Junior P3


Proof Based Problems  


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Solution

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$x^2-12y+4=0\implies x^2=12y-4$

$12y-4\equiv 2(\text{mod} 3)$ 

$ \implies x^2\equiv 2(\text{mod} 3)$


Case 1: $x\equiv 0(\text{mod} 3)\implies x^2\equiv 0(\text{mod} 3)$

Case 2: $x\equiv 1(\text{mod} 3)\implies x^2\equiv 1(\text{mod} 3)$

Case 3: $x\equiv 2(\text{mod} 3)\implies x^2\equiv 1(\text{mod} 3)$


But, we know that $x^2\equiv 2(\text{mod} 3)$


So, this is a contradiction.


$\therefore$ There are no solutions to the given equation.

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