Question

If A = (\begin{bmatrix} -1 & -2& -2 \[0.3em] 2&1 &-2 \[0.3em] 2 &-2 & 1 \end{bmatrix}), show that adj A = 3AT

Answer 1

Given as

A =

Co-factors of A are

C11 = – 3

C21 = 6

C31 = 6

C12 = – 6

C22 = 3

C32 = – 6

C13 = – 6

C23 = – 6

C33 = 3

adj A = 3AT

Hence proved.