A =

Cofactors of A

C₁₁ = – 22 C₂₁ = 11 C₃₁ = – 11

C₁₂ = 4 C₂₂ = – 2 C₃₂ = 2

C₁₃ = 16 C₂₃ = – 8 C₃₃ = 8

adj A =

=

adj A =

Now, (adj A).A =

=

=

Also, |A|.I =

= [2( – 2 – 20) + 1( – 4 – 0) + 3(16 – 0)]

= ( – 44 – 4 + 48)

=

Then, A.(adj A) =

=

=

Hence, (adj A).A = |A|.I = A(adj A)