Let A = [[a11,a12],[a21,a22]] and B = [[b11,b12],[b21,b22]] be two matrices such that A*B = I. Let C = A^(-1) and D = B^(-1). Express the elements of D in terms of the elements of B.

GATE 1996 · Engineering Mathematics · Matrix · medium

Answer: D = B^(-1) = A = [[b22, -b12], [-b21, b11]] / (b11*b22 - b12*b21).

  1. Recognize inverse relationship from AB = I: Since AB = I, matrix A is the inverse of B. Therefore D = B^(-1) = A.
  2. Apply 2x2 inverse formula to express D in terms of B: det(B) = b11*b22 - b12*b21. D = B^(-1) = [[b22/(det B), -b12/(det B)], [-b21/(det B), b11/(det B)]].