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Reviewed CSCA Mathematics question · Hard

Solve the inequality (x^2 - 2x - 8) / (x + 3) < 0. Which of the following is the solution set?

  1. (-∞, -4) ∪ (-3, 2)
  2. (-4, -3) ∪ (2, ∞)
  3. (-∞, -4) ∪ (2, ∞)
  4. (-3, 2)
Show the answer and explanation

Correct answer

A. (-∞, -4) ∪ (-3, 2)

Principle or equation

For a rational inequality, find critical points where numerator or denominator is zero, then test intervals on the number line.

Why this answer is correct

Factor numerator: x^2 - 2x - 8 = (x - 4)(x + 2). Critical points: x = -2, 4, and x = -3 (denominator zero). Test intervals: (-∞, -4), (-4, -3), (-3, 2), (2, 4), (4, ∞). The inequality is < 0 on (-∞, -4) and (-3, 2).

Example

For (x^2 - 1)/(x - 2) < 0, critical points -1, 1, 2; solution (-∞, -1) ∪ (1, 2).

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