Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 8 - Section 8.3 - Matrix Operations and Their Applications - Exercise Set - Page 920: 78

Answer

The statement does not make sense. The correct statement is, “The $m\times n$ matrix and an $n\times p$ matrix are multiplied by multiplying corresponding elements and then adding them.”

Work Step by Step

The product of two matrices is defined as below: Consider a matrix A of $m\times n$ order and another matrix B of $n\times p$ order. To find the ${{i}^{th}}$ row and ${{j}^{th}}$ column of the product AB, each element in the ${{i}^{th}}$ row of A is multiplied by the corresponding element in the ${{j}^{th}}$ column of B, and then these products are added. The product matrix AB is an $m\times p$ order matrix, that is, if $A={{\left[ {{a}_{ij}} \right]}_{m\times n}}$ and $B={{\left[ {{b}_{jp}} \right]}_{n\times p}}$, then $\begin{align} & AB=C \\ & C={{\left[ {{c}_{ip}} \right]}_{m\times p}} \end{align}$ Here, ${{c}_{ip}}=\sum\limits_{j=1}^{n}{{{a}_{ij}}{{b}_{jp}}}$ Let $A={{\left[ \begin{matrix} a & b \\ c & d \\ \end{matrix} \right]}_{2\times 2}}$ and $X={{\left[ \begin{matrix} x \\ y \\ \end{matrix} \right]}_{2\times 1}}$, then $\begin{align} & AX={{\left[ \begin{matrix} a & b \\ c & d \\ \end{matrix} \right]}_{2\times 2}}{{\left[ \begin{matrix} x \\ y \\ \end{matrix} \right]}_{2\times 1}} \\ & ={{\left[ \begin{matrix} ax+by \\ cx+dy \\ \end{matrix} \right]}_{2\times 1}} \end{align}$ The matrix multiplication cannot be performed by simply multiplying the elements. The elements are then added. Therefore, the statement does not make sense. The correct statement is, “The $m\times n$ matrix and an $n\times p$ matrix are multiplied by multiplying corresponding elements and then adding them.”
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.