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WAEC Further Mathematics 2026 Question 5

Question 5

Matrices and Determinants

Given that P = (3 5 −4 / 6 −3 −5 / −2 2 1) and Q = (−3 −2 1 / 1 2 3 / 3 1 2), find |P + Q|. (Each matrix is written row by row; / separates the rows.)

  1. A.169
  2. B.135
  3. C.−135
  4. D.−169
Show the answer and explanation

Answer: C (−135)

Explanation

P + Q = (0 3 −3 / 7 −1 −2 / 1 3 3). Expanding along the first row: 0 − 3(7×3 − (−2)×1) + (−3)(7×3 − (−1)×1) = −3(23) − 3(22) = −69 − 66 = −135.