Solve the following system of equations by matrix method:

x + y + z = 6


x + 2z = 17


3x + y + z = 12


The given system can be written in matrix form as:



A X = B


Now, |A| = 1


= 1(– 2) – 1(1 – 6) + 1(1)


= – 2 + 5 + 1


= 4


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


X = A – 1B


Cofactors of A are:


C11 = (– 1)1 + 1 0 – 2 = – 2


C21 = (– 1)2 + 1 1 – 1 = 0


C31 = (– 1)3 + 1 2 – 0 = 2


C12 = (– 1)1 + 2 1 – 6 = 5


C22 = (– 1)2 + 1 1 – 3 = – 2


C32 = (– 1)3 + 1 2 – 1 = – 1


C13 = (– 1)1 + 2 1 – 0 = 1


C23 = (– 1)2 + 1 1 – 3 = 2


C33 = (– 1)3 + 1 0 – 1 = – 1


adj A =


=


A – 1 =


Now, X = A – 1B =


X =


X =


X =


Hence, X = 3,Y = 1 and Z = 2


2