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JAMB Mathematics 2006 Question 49

Question 49

Inequalities

If y = x2 − x − 12, find the range of values of x for which y ≥ 0.

  1. A.x < −3 or x > 4
  2. B.x ≤ −3 or x ≥ 4
  3. C.−3 < x ≤ 4
  4. D.−3 ≤ x ≤ 4
Show the answer and explanation

Answer: B (x ≤ −3 or x ≥ 4)

Explanation

y = (x + 3)(x − 4), which is zero at −3 and 4 and positive outside them, so y ≥ 0 for x ≤ −3 or x ≥ 4.