A =

Cofactors of A

C₁₁ = 30 C₂₁ = 12 C₃₁ = – 3

C₁₂ = – 20 C₂₂ = – 8 C₃₂ = 2

C₁₃ = – 50 C₂₃ = – 2 0 C₃₃ = 5

adj A =

=

So, adj(A) =

Now, A.(adj A) =

=

=

Hence, A(adj A) = 0