Solving 3×3 Linear Systems with Matrices: Inconsistent Systems and No Solutions

In the realm of linear algebra, systems of equations play a pivotal role. A system of linear equations comprises multiple equations with multiple variables, and our goal is to find values for these variables that satisfy all equations simultaneously. One powerful tool for solving such systems is the use of matrices.

What are Inconsistent Systems?

An inconsistent system of equations is a system where there exists no solution that can satisfy all equations simultaneously. This means that the equations are contradictory, and no set of values for the variables can make all equations true.

Identifying Inconsistent Systems

When solving a system of linear equations using matrices, we can identify inconsistent systems by observing the following:

• Row of Zeros with a Non-Zero Constant: If, after performing row operations on the augmented matrix, we obtain a row with all zeros in the coefficient matrix and a non-zero value in the constant column, the system is inconsistent.
• Contradictory Equations: Sometimes, inconsistent systems can be identified directly from the equations themselves. If two equations contradict each other, no solution can satisfy both. For example, the equations x + y = 5 and x + y = 7 contradict each other.

Example: Solving an Inconsistent System

Let’s consider the following system of equations:

x + 2y – z = 1
2x – y + z = 2
3x + y – 2z = 3

To solve this system using matrices, we first construct the augmented matrix:

[ 1 2 -1 | 1 ]
[ 2 -1 1 | 2 ]
[ 3 1 -2 | 3 ]

Now, we perform row operations to transform the matrix into row-echelon form. Here’s a possible sequence of operations:

1. R2 – 2R1 -> R2
2. R3 – 3R1 -> R3
3. R3 + 5R2 -> R3

After these operations, the augmented matrix becomes:

[ 1 2 -1 | 1 ]
[ 0 -5 3 | 0 ]
[ 0 0 0 | 3 ]

Notice that the last row has all zeros in the coefficient matrix but a non-zero value (3) in the constant column. This indicates that the system is inconsistent. There is no solution that can satisfy all three equations simultaneously.

Geometric Interpretation

In three-dimensional space, each equation in a system of three linear equations represents a plane. An inconsistent system corresponds to a situation where the three planes do not intersect at a single point. They could be parallel or intersect in a way that creates a line but not a single point.

Conclusion

Understanding inconsistent systems is crucial when working with systems of linear equations. The ability to identify and interpret inconsistent systems using matrices provides a valuable tool for solving real-world problems that involve multiple variables and constraints.