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JAMB Mathematics 2004 Question 22

Question 22

Matrices and Determinants

The inverse of the matrix (2 1; 1 1) is (matrices written row by row)

  1. A.(1 1; −1 2)
  2. B.(1 −1; 1 2)
  3. C.(1 1; 1 2)
  4. D.(1 −1; −1 2)
Show the answer and explanation

Answer: D ((1 −1; −1 2))

Explanation

The determinant is 2 − 1 = 1. Swap the diagonal entries and change the signs of the others: (1 −1; −1 2).