Q. 11

If A – 1 = and , find (AB) – 1.(CBSE 2012)

Answer :

A – 1 = B =


|B| = 1(3 – 0) – 2( – 1 – 0) – 2(2 – 0)


= 3 + 2 – 4


|B| = 1


Now, B – 1 =


Cofactors of B are:


C11 = – 3 C21 = 2 C31 = 6


C12 = 1 C22 = 1 C32 = 2


C13 = 2 C23 = 2 C33 = 5


adj B =


=


So, adj B =


Now, B – 1 =


(AB) – 1 = B – 1 A – 1



=


Hence, =

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