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JAMB Mathematics 2009 Question 23

Question 23

Matrices and Determinants

If P = (x + 3 x + 2; x + 1 x − 1), evaluate x if |P| = −10. (Matrix written row by row.)

  1. A.−5
  2. B.−2
  3. C.2
  4. D.5
Show the answer and explanation

Answer: D (5)

Explanation

|P| = (x + 3)(x − 1) − (x + 2)(x + 1) = (x2 + 2x − 3) − (x2 + 3x + 2) = −x − 5. So −x − 5 = −10 and x = 5.