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JAMB Mathematics 2014 Question 22

Question 22

Matrices and Determinants

Find y, if (5 −6 / 2 −7)(x / y) = (7 / −11)
(the first matrix has rows 5, −6 and 2, −7; the column vectors are (x, y) and (7, −11))

  1. A.2
  2. B.8
  3. C.5
  4. D.3
Show the answer and explanation

Answer: D (3)

Explanation

The equations are 5x − 6y = 7 and 2x − 7y = −11. Doubling the first and multiplying the second by 5 gives 10x − 12y = 14 and 10x − 35y = −55; subtracting, 23y = 69, so y = 3.