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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 23

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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1
Identify the dimensions of matrices B and D. For matrix multiplication BD to be defined, the number of columns in B must equal the number of rows in D.
Write down the dimensions of B as \(m \times n\) and D as \(p \times q\). Check if \(n = p\) to confirm if multiplication BD is possible.
If the multiplication is defined, set up the product matrix BD, which will have dimensions \(m \times q\).
Calculate each element of the product matrix BD by taking the dot product of the corresponding row of B and column of D. Specifically, the element in row \(i\) and column \(j\) of BD is given by \(\sum_{k=1}^n B_{ik} \times D_{kj}\).
If the multiplication is not defined because the inner dimensions do not match, state that the operation BD is not defined due to incompatible matrix dimensions.

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Key Concepts

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

Matrix Multiplication

Matrix multiplication involves multiplying rows of the first matrix by columns of the second matrix and summing the products. The operation is only defined when the number of columns in the first matrix equals the number of rows in the second matrix.
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Dimensions of Matrices

The dimensions of a matrix are given as rows × columns. Understanding matrix dimensions is crucial to determine if operations like multiplication are possible and to predict the size of the resulting matrix.
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Undefined Matrix Operations

Some matrix operations are undefined if dimension requirements are not met. For example, if the number of columns in the first matrix does not equal the number of rows in the second, multiplication cannot be performed.
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In Exercises 1 - 24, use Gaussian Elimination to find the complete solution to each system of equations, or show that none exists. {w+2x+3yz=72x3y+z=4w4x+y=3\(\begin{cases}\)w + 2x + 3y - z = 7 \\2x - 3y + z = 4 \(\w\) - 4x + y = 3\(\end{cases}\)

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

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Textbook Question

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