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JAMB Mathematics 2011 Question 20

Question 20

Inequalities

Solve the inequalities x2 + 2x > 15.

  1. A.x < −3 or x > 5
  2. B.−5 < x < 3
  3. C.x < 3 or x > 5
  4. D.x > 3 or x < −5
Show the answer and explanation

Answer: D (x > 3 or x < −5)

Explanation

x2 + 2x − 15 = (x + 5)(x − 3) > 0 when both factors have the same sign: x > 3 or x < −5.