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WAEC Mathematics 2014 Question 12

Question 12

Quadratic Equations

Find the truth set of the equation x2 = 3(2x + 9).

  1. A.{x : x = 3, x = 9}
  2. B.{x : x = −3, x = −9}
  3. C.{x : x = 3, x = −9}
  4. D.{x : x = −3, x = 9}
Show the answer and explanation

Answer: D ({x : x = −3, x = 9})

Explanation

x2 − 6x − 27 = 0 factorises as (x − 9)(x + 3) = 0, so x = 9 or x = −3.