Chapter 8: Problem 58
Write the system of linear equations as a matrix equation, \(A X=B,\) and (b) use Gauss-Jordan elimination on \(A : B\) to solve for the matrix \(X .\) $$\left\\{\begin{aligned} 2 x_{1}+3 x_{2} &=5 \\ x_{1}+4 x_{2} &=10 \end{aligned}\right.$$
Short Answer
Expert verified
The solution for the system of equations using matrix form and Gauss-Jordan elimination is \(x_1 = -2\) and \(x_2 = 3\).
Step by step solution
01
Transform the system of equations into matrix form
To transform the system of linear equations into the matrix \(A X = B\), we first must identify the coefficients of the variables on the left-hand side of the equations. These will make up matrix \(A\). The variables \(x_1\) and \(x_2\) will constitute the column matrix \(X\), and the constants on the right-hand side of the equations will form column matrix \(B\). Thus, we get: \[A=\begin{bmatrix} 2 & 3 \\ 1 & 4 \end{bmatrix}, X=\begin{bmatrix} x_1 \\ x_2 \end{bmatrix}, B=\begin{bmatrix} 5 \\ 10 \end{bmatrix}\] Hence, the matrix equation \(A X= B\) becomes: \[\begin{bmatrix} 2 & 3 \\ 1 & 4 \end{bmatrix} \begin{bmatrix} x_1 \\ x_2 \end{bmatrix} = \begin{bmatrix} 5 \\ 10 \end{bmatrix}\]
02
Apply the Gauss-Jordan method
We can use Gauss-Jordan elimination to solve this system. This method involves forming an augmented matrix \(A | B\) and then applying row operations to reach a final form where the solution becomes evident. The augmented matrix for our system is: \[\begin{bmatrix} 2 & 3 & 5 \\ 1 & 4 & 10 \end{bmatrix}\] The main goal of Gauss-Jordan is to create a matrix in reduced row echelon form. We'll start by dividing the first row by 2 for simplicity: \[\begin{bmatrix} 1 & 1.5 & 2.5 \\ 1 & 4 & 10 \end{bmatrix}\] and next, we subtract the first row from the second to eliminate \(x_1\) from the second equation: \[\begin{bmatrix} 1 & 1.5 & 2.5 \\ 0 & 2.5 & 7.5 \end{bmatrix}\] Dividing the second row by 2.5, we yield: \[\begin{bmatrix} 1 & 1.5 & 2.5 \\ 0 & 1 & 3 \end{bmatrix}\] Finally, to eliminate \(x_2\) from the first equation, we subtract 1.5 times the second row from the first: \[\begin{bmatrix} 1 & 0 & -2 \\ 0 & 1 & 3 \end{bmatrix}\] From this we can read off the solutions.
03
Extract the solutions
From the last matrix, reading off the solutions, we get \(x_1 = -2\) and \(x_2 = 3\) correspondingly, forming the solution set for the original system of equations.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Matrix Equation
A matrix equation is a way to represent a system of linear equations using matrix notation. This is useful because matrices allow us to use systematic methods for solving complex systems. To write a system of equations as a matrix equation like \(A X = B\), we need to do the following:
- Identify Coefficients: These form the matrix \(A\). For the system \(2x_1 + 3x_2 = 5\) and \(x_1 + 4x_2 = 10\), the coefficients of \(x_1\) and \(x_2\) create the matrix \(A\): \[A = \begin{bmatrix} 2 & 3 \ 1 & 4 \end{bmatrix}\]
- Form the Variable Matrix: The variables \(x_1\) and \(x_2\) are placed in a column matrix \(X\):\[X = \begin{bmatrix} x_1 \ x_2 \end{bmatrix}\]
- Combine Constants: These are the known values, forming matrix \(B\):\[B = \begin{bmatrix} 5 \ 10 \end{bmatrix}\]
System of Linear Equations
A system of linear equations is a set of equations where each equation is linear, meaning it graphs as a straight line. In mathematics, solving these systems is crucial because it allows us to find the point(s) where the lines intersect, which represents the solution.
A simple example is the system:
Depending on the number of solutions:
A simple example is the system:
- Equation 1: \(2x_1 + 3x_2 = 5\)
- Equation 2: \(x_1 + 4x_2 = 10\)
Depending on the number of solutions:
- Unique Solution: If lines intersect at one point, as in this example where the solution is \(x_1 = -2\) and \(x_2 = 3\).
- No Solution: If the lines are parallel, they never intersect.
- Infinitely Many Solutions: If the lines overlap, every point on the line is a solution.
Reduced Row Echelon Form
Reduced row echelon form (RREF) is a special type of matrix that results from using the Gauss-Jordan elimination method. It's the simplest form we can reduce a matrix to, which makes it easy to read off solutions to a system of equations. In RREF:
Through a series of row operations, we transform it to:\[\begin{bmatrix} 1 & 0 & -2 \ 0 & 1 & 3 \end{bmatrix}\]
In this form, it's clear that \(x_1 = -2\) and \(x_2 = 3\). Every step in reaching this form simplifies the matrix, making the solutions more transparent. Successfully manipulating a matrix to RREF ensures we've correctly solved the system.
- Each leading 1 in a row is the only non-zero entry in its column.
- The leading 1 of each row appears to the right of the leading 1 in the row above it.
- Rows with all zeroes, if any, are at the bottom of the matrix.
Through a series of row operations, we transform it to:\[\begin{bmatrix} 1 & 0 & -2 \ 0 & 1 & 3 \end{bmatrix}\]
In this form, it's clear that \(x_1 = -2\) and \(x_2 = 3\). Every step in reaching this form simplifies the matrix, making the solutions more transparent. Successfully manipulating a matrix to RREF ensures we've correctly solved the system.