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