Maths Olympiad Prep

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Algebra Difficulty 5.0 AIME Prove it Ukraine

Find all pairs of integers (x,y)(x, y) that satisfy the following equality:
x+x+xyyy=2011. |x+|x+|x|| \cdot ||-y|-y|-y|=2011.

Solution

Since 20112011 is a prime number, every multiple of the left-hand side must be equal to either 11 or 20112011.
If x0x \ge 0, the first multiple equals 3x3x, and there are no solutions. Similarly, there are no solutions if y0y \le 0 (the second multiple is 3y-3y).
Suppose now that x<0x < 0 and y>0y > 0. Then
x+x+xyyy=x+xxyyy=xy=xy=2011. |x+|x+|x|| \cdot ||-y|-y|-y|=|x+|x-x|| \cdot ||y-y|-y|=|x| \cdot |-y| = -xy = -2011.
Recalling that 20112011 is prime, we get the above answers.

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