Solve the following system of equations by matrix method:

2x + y + z = 2


x + 3y –z = 5


3x + y – 2z = 6


The given system can be written in matrix form as:


or A X = B


A = , X = and B =


Now, |A| = 2


= 2(– 6 + 1) – 1(– 2 + 3) + 1(1 – 9)


= – 10 – 1 – 8


= – 19


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


X = A – 1B


Cofactors of A are:


C11 = (– 1)1 + 1 – 6 + 1 = – 5


C21 = (– 1)2 + 1(24 + 4) = – 28


C31 = (– 1)3 + 1 – 1 – 3 = – 4


C12 = (– 1)1 + 2 – 2 + 3 = – 1


C22 = (– 1)2 + 1 – 4 – 3 = – 7


C32 = (– 1)3 + 1 – 2 – 1 = 3


C13 = (– 1)1 + 21 – 9 = – 8


C23 = (– 1)2 + 12 – 3 = – 1


C33 = (– 1)3 + 1 6 – 1 = 5


adj A =


=


A – 1 =


Now, X = A – 1B =


X =


X =


X =


Hence, X = 1,Y = 1 and Z = – 1


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