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JAMB Mathematics 1978 Question 14

Question 14

Inequalities

If y = 2x2 + 9x − 35, find the range of values for which y < 0.

  1. A.−7 < x < 5/2
  2. B.−7 ≤ x < 5
  3. C.−5 ≤ x < 7
  4. D.−7/2 < x ≤ 5.
  5. E.None of the above.
Show the answer and explanation

Answer: A (−7 < x < 5/2)

Explanation

2x² + 9x − 35 = (2x − 5)(x + 7), which is zero at x = −7 and x = 5/2. The parabola opens upwards, so it is negative between the roots.