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WAEC Further Mathematics 2008 Question 9

Question 9

Polynomials

Which of the following quadratic curves will not intersect with the x-axis?

  1. A.y = 2 − 4x − x2
  2. B.y = x2 − 5x − 1
  3. C.y = 2x2 − x − 1
  4. D.y = 3x2 − 2x + 4
Show the answer and explanation

Answer: D (y = 3x2 − 2x + 4)

Explanation

A curve misses the x-axis when b2 − 4ac < 0. For 3x2 − 2x + 4: 4 − 48 = −44 < 0; the others have positive discriminants.