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Ch. 6 - Matrices and Determinants
Blitzer - College Algebra 8th Edition
Blitzer8th EditionCollege AlgebraISBN: 9780136970514Not the one you use?Change textbook
Chapter 7, Problem 21

Solve each system of equations using matrices. Use Gaussian elimination with back-substitution or Gauss-Jordan elimination.
{x+yz=22xy+z=5x+2y+2z=1\(\begin{cases}\)x + y - z = -2 \\2x - y + z = 5 \\-x + 2y + 2z = 1\(\end{cases}\)

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Write the system of equations as an augmented matrix. The system is: \(x + y - z = -2\) \$2x - y + z = 5$ \(-x + 2y + 2z = 1\) The augmented matrix is: \[\begin{bmatrix} 1 & 1 & -1 & | & -2 \\ 2 & -1 & 1 & | & 5 \\ -1 & 2 & 2 & | & 1 \end{bmatrix}\]
Use Gaussian elimination to transform the matrix into an upper triangular form. Start by using the first row to eliminate the \(x\)-terms in the second and third rows: - For row 2: Replace row 2 with (row 2) - 2*(row 1). - For row 3: Replace row 3 with (row 3) + (row 1).
After these operations, the matrix will have zeros below the leading 1 in the first column. Next, use the second row to eliminate the \(y\)-term in the third row by replacing row 3 with (row 3) - (appropriate multiple of row 2) to get a zero in the second column of row 3.
Once the matrix is in upper triangular form, use back-substitution to solve for the variables starting from the last row. Solve for \(z\) from the third row, then substitute back into the second row to find \(y\), and finally substitute \(y\) and \(z\) into the first row to find \(x\).
Alternatively, you can continue with Gauss-Jordan elimination by making the matrix into reduced row echelon form (RREF) by creating leading 1s and zeros above and below each pivot, which directly gives the solution for \(x\), \(y\), and \(z\).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Systems of Linear Equations

A system of linear equations consists of multiple linear equations involving the same set of variables. The goal is to find values for the variables that satisfy all equations simultaneously. Understanding how to represent and interpret these systems is fundamental before applying matrix methods.
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Matrix Representation of Systems

Systems of linear equations can be expressed in matrix form as AX = B, where A is the coefficient matrix, X is the column matrix of variables, and B is the constants matrix. This representation simplifies the use of matrix operations to solve the system efficiently.
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Gaussian Elimination and Gauss-Jordan Elimination

Gaussian elimination transforms the augmented matrix into an upper triangular form to solve via back-substitution, while Gauss-Jordan elimination reduces it further to reduced row echelon form for direct solution. Both methods use row operations to systematically solve linear systems.
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Related Practice
Textbook Question

In Exercises 1 - 24, use Gaussian Elimination to find the complete solution to each system of equations, or show that none exists. {w+xy+z=22wx+2yz=7w+2x+y+2z=1\(\begin{cases}\)w + x - y + z = -2 \\2w - x + 2y - z = 7 \\-w + 2x + y + 2z = -1\(\end{cases}\)

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Textbook Question

For Exercises 11–22, use Cramer's Rule to solve each system. {2x=3y+25x=514y\(\begin{cases}\)2x = 3y + 2 \\5x = 51 - 4y\(\end{cases}\)

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Textbook Question

In Exercises 23–30, use expansion by minors to evaluate each determinant. 300215251\(\begin{vmatrix}\)3 & 0 & 0 \\2 & 1 & -5 \\2 & 5 & -1\(\end{vmatrix}\)

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Textbook Question

Perform the indicated matrix operations given that and D are defined as follows. If an operation is not defined, state the reason. BD

A=[212531]B=[023215]C=[123112121]D=[231324]A=\(\begin{bmatrix}\)2 & -1 & 2\\ 5 & 3 & -1\(\end{bmatrix}\[\quad\) B=\(\begin{bmatrix}\)0 & -2\\ 3 & 2\\ 1 & -5\(\end{bmatrix}\)C=\(\begin{bmatrix}\)1 & 2 & 3\\ -1 & 1 & 2\\ -1 & 2 & 1\(\end{bmatrix}\]\quad\) D=\(\begin{bmatrix}\)-2 & 3 & 1\\ 3 & -2 & 4\(\end{bmatrix}\)

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Textbook Question

Solve each system of equations using matrices. Use Gaussian elimination with back-substitution or Gauss-Jordan elimination.

{x+3y=0x+y+z=13xyz=11\(\begin{cases}\)x + 3y = 0 \(\x\) + y + z = 1 \\3x - y - z = 11\(\end{cases}\)

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Textbook Question

Let A=[372950]A = \(\begin{bmatrix}\)-3 & -7 \\2 & -9 \\5 & 0\(\end{bmatrix}\) and B=[510034]B = \(\begin{bmatrix}\)-5 & -1 \\0 & 0 \\3 & -4\(\end{bmatrix}\). Solve each matrix equation for X. 3X + 2A = B

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