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In this section, you will:
  • Write the augmented matrix of a system of equations.
  • Write the system of equations from an augmented matrix.
  • Perform row operations on a matrix.
  • Solve a system of linear equations using matrices.
German mathematician Carl Friedrich Gauss (1777–1855).

Carl Friedrich Gauss lived during the late 18th century and early 19th century, but he is still considered one of the most prolific mathematicians in history. His contributions to the science of mathematics and physics span fields such as algebra, number theory, analysis, differential geometry, astronomy, and optics, among others. His discoveries regarding matrix theory changed the way mathematicians have worked for the last two centuries.

We first encountered Gaussian elimination in Systems of Linear Equations: Two Variables . In this section, we will revisit this technique for solving systems, this time using matrices.

Writing the augmented matrix of a system of equations

A matrix    can serve as a device for representing and solving a system of equations. To express a system in matrix form, we extract the coefficients of the variables and the constants, and these become the entries of the matrix. We use a vertical line to separate the coefficient entries from the constants, essentially replacing the equal signs. When a system is written in this form, we call it an augmented matrix    .

For example, consider the following 2 × 2 system of equations.

3 x + 4 y = 7 4 x −2 y = 5

We can write this system as an augmented matrix:

[ 3 4 4 −2    |    7 5 ]

We can also write a matrix containing just the coefficients. This is called the coefficient matrix    .

[ 3 4 4 −2 ]

A three-by-three system of equations such as

3 x y z = 0          x + y = 5      2 x −3 z = 2

has a coefficient matrix

[ 3 −1 −1 1 1 0 2 0 −3 ]

and is represented by the augmented matrix

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

Notice that the matrix is written so that the variables line up in their own columns: x -terms go in the first column, y -terms in the second column, and z -terms in the third column. It is very important that each equation is written in standard form a x + b y + c z = d so that the variables line up. When there is a missing variable term in an equation, the coefficient is 0.

Given a system of equations, write an augmented matrix.

  1. Write the coefficients of the x -terms as the numbers down the first column.
  2. Write the coefficients of the y -terms as the numbers down the second column.
  3. If there are z -terms, write the coefficients as the numbers down the third column.
  4. Draw a vertical line and write the constants to the right of the line.

Writing the augmented matrix for a system of equations

Write the augmented matrix for the given system of equations.

    x + 2 y z = 3   2 x y + 2 z = 6    x 3 y + 3 z = 4

The augmented matrix displays the coefficients of the variables, and an additional column for the constants.

[ 1 2 −1 2 −1 2 1 −3 3    |    3 6 4 ]
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Write the augmented matrix of the given system of equations.

4 x −3 y = 11 3 x + 2 y = 4

[ 4 −3 3 2 | 11 4 ]

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Writing a system of equations from an augmented matrix

We can use augmented matrices to help us solve systems of equations because they simplify operations when the systems are not encumbered by the variables. However, it is important to understand how to move back and forth between formats in order to make finding solutions smoother and more intuitive. Here, we will use the information in an augmented matrix to write the system of equations in standard form.

Questions & Answers

given eccentricity and a point find the equiation
Moses Reply
12, 17, 22.... 25th term
Alexandra Reply
12, 17, 22.... 25th term
Akash
College algebra is really hard?
Shirleen Reply
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Carole
find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
salma
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
Abhi
how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
hmm
Abhi
is it a question of log
Abhi
🤔.
Abhi
I rally confuse this number And equations too I need exactly help
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salma
Commplementary angles
Idrissa Reply
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Sherica
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Sherica
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Tamia
hii
Uday
hi
salma
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
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Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Practice Key Terms 7

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Source:  OpenStax, College algebra. OpenStax CNX. Feb 06, 2015 Download for free at https://legacy.cnx.org/content/col11759/1.3
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