Let A be an invertible n x n matrix, and let B be an n x p matrix.
(a) Show that A^(-1)B is a solution of the matrix equation AX = B, and that A^(-1)B is the unique solution of AX = B.
(b) Use elementary matrices to show that any sequence of elementary row operations that reduces A to I also transforms B into A^(-1)B:
If [A B] ~ ... ~ [I X], then X = A^(-1)B.
Comment: In applications, if A is larger than 2 x 2, then finding A^(-1)B by row reducing [A B] is much faster than computing both A^(-1) and A^(-1)B.