Absolute Value Equation Integer Solutions

CAT 2023 Slot 1 · Quantitative Ability · Medium · Algebra

The number of integer solutions of equation 2∣x∣(x2+1)=5x22|x|(x^2 + 1) = 5x^2 is

Answer

3

Explanation

  1. x=0x = 0 is a solution since 2(0)(1)=5(0)2=02(0)(1) = 5(0)^2 = 0.
  2. If x≠0x \neq 0, then ∣x∣>0|x| > 0. Divide both sides by ∣x∣|x| (noting x2=∣x∣2x^2 = |x|^2): 2(x2+1)=5∣x∣2(x^2 + 1) = 5|x| 2∣x∣2−5∣x∣+2=02|x|^2 - 5|x| + 2 = 0 (2∣x∣−1)(∣x∣−2)=0(2|x| - 1)(|x| - 2) = 0 So ∣x∣=12|x| = \frac{1}{2} or ∣x∣=2|x| = 2.

Since xx must be an integer:

  • ∣x∣=12|x| = \frac{1}{2} gives no integer solutions.
  • ∣x∣=2|x| = 2 gives x=2x = 2 and x=−2x = -2.

Thus, the integer solutions are x=0,2,−2x = 0, 2, -2, making a total of 3 solutions.

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