Solve the following system of equations by matrix method:

x + y + z = 3


2x – y + z = – 1


2x + y – 3z = – 9

The given system can be written in matrix form as:


or A X = B


A = , X = and B =


Now, |A| = 1


= (3 – 1) – 1(– 6 – 2) + 1(2 + 2)


= 2 + 8 + 4


= 14


So, the above system has a unique solution, given by


X = A – 1B


Cofactors of A are:


C11 = (– 1)1 + 1 3 – 1 = 2


C21 = (– 1)2 + 1 – 3 – 1 = 4


C31 = (– 1)3 + 1 1 + 1 = 2


C12 = (– 1)1 + 2 – 6 – 2 = 8


C22 = (– 1)2 + 1 – 3 – 2 = – 5


C32 = (– 1)3 + 1 1 – 2 = 1


C13 = (– 1)1 + 2 2 + 2 = 4


C23 = (– 1)2 + 1 1 – 2 = 1


C33 = (– 1)3 + 1 – 1 – 2 = – 3


adj A =


=


Now, X = A – 1B =


X =


X =


Hence, X = ,Y = and Z =


2