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Real game with a computer

Source: Indonesian National Science Olympiad 2018, Mathematics P4

July 6, 2018
algebra

Problem Statement

In a game, Andi and a computer take turns. At the beginning, the computer shows a polynomial x2+mx+nx^2 + mx + n where m,n∈Zm,n \in \mathbb{Z}, such that it doesn't have real roots. Andi then begins the game. On his turn, Andi may change a polynomial in the form x2+ax+bx^2 + ax + b into either x2+(a+b)x+bx^2 + (a+b)x + b or x2+ax+(a+b)x^2 + ax + (a+b). However, Andi may only choose a polynomial that has real roots. On the computer's turn, it simply switches the coefficient of xx and the constant of the polynomial. Andi loses if he can't continue to play. Find all (m,n)(m,n) such that Andi always loses (in finitely many turns).