Absolute Value Equation Integer Solutions

CAT 2023 Slot 1 · QA · Medium · Algebra

The number of integer solutions of equation 2x(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 x0x \neq 0, then x>0|x| > 0. Divide both sides by x|x| (noting x2=x2x^2 = |x|^2): 2(x2+1)=5x2(x^2 + 1) = 5|x| 2x25x+2=02|x|^2 - 5|x| + 2 = 0 (2x1)(x2)=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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