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JAMB Mathematics 2007 Question 19

Question 19

Inequalities

The solution of the quadratic inequality (x2 + x − 12) ≥ 0 is

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

Answer: D (x ≥ 3 or x ≤ −4)

Explanation

x2 + x − 12 = (x + 4)(x − 3), which is zero at −4 and 3 and positive outside them: x ≥ 3 or x ≤ −4.