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WAEC Further Mathematics 2015 Question 28

Question 28

Matrices and Determinants

If |1 + 2x, −1 / 6, 3 − x| = −3, find the values of x. (Determinant written row by row; / separates the rows.)

  1. A.x = 3, −2
  2. B.x = 4, −2/3
  3. C.x = −4, 3/2
  4. D.x = 4, −3/2
Show the answer and explanation

Answer: D (x = 4, −3/2)

Explanation

(1 + 2x)(3 − x) + 6 = −3 gives 2x² − 5x − 12 = 0, (2x + 3)(x − 4) = 0: x = 4 or −3/2.