how to do the question D, please explain thanks

(1) (after 5.1) This exercise uses the notion of cofactors of a matrix A to nd a formula for the inverse A'l. Recall that if A is an n X n matrix, then Mij denotes the matrix obtained from A by deleting the ith row and jth column of A. 2 0 2 LetA= 1 1 1 . 3 1 5 (a) Compute all nine cofactors of A, as well as det(A). Let B be the 3 X 3 matrix containing the cofactors, with each entry multiplied by the appropriate :I: sign. So the ijentry of B is (1)\"'+j det(M2-j). (b) Compute ABT. You should get a diagonal matrix with the same number in every diagonal entry, in other words, I multiple of the identity matrix. What multiple is it (in terms of A)? (0) Fill in the blank (with a scalar) to make this equation true: ABT = ( ? ) -I, therefore A'1 = L -BT. (1?) ((1) Compute the matrix BT when A is the 2 x 2 matrix a b A - [a d] , and then use it to compute a formula for A'l. Does this agree with the formula for A'1 given in the textbook? 1