College Algebra (11th Edition)

Published by Pearson
ISBN 10: 0321671791
ISBN 13: 978-0-32167-179-0

Chapter 5 - Section 5.8 - Matrix Inverses - 5.8 Exercises - Page 565: 5

Answer

The given matrices are ${NOT}$ inverses of each other.

Work Step by Step

We know that when two matrices will be inverses of each other, then their products are called as the identity matrix $(I)$. Suppose $P$ and $Q$ consist of $n \times n$ matrix form, then $P$ and $Q$ are inverse of each other if $PQ=I_n$ and $QP=I_n$ Here, we have: $P=\begin{bmatrix} -1 & 2 \\ 3 & -5 \end{bmatrix}$ and $Q=\begin{bmatrix} -5 & -2 \\ -3 & -1 \end{bmatrix} $ . As we can see that both matrices of the same dimensions, that is, $2 \times 2$ or, n=2. Thus, we can multiply them easily. $PQ=\begin{bmatrix} -1 & 2 \\ 3 & -5 \end{bmatrix} \begin{bmatrix} -5 & -2 \\ -3 & -1 \end{bmatrix}$ Using multiplication method, it follows that $PQ =\begin{bmatrix} -1 & 0 \\ 0 & -1 \end{bmatrix} $ This implies that the given matrices are ${NOT}$ inverses of each other because $PQ \neq I_2$, that is, their products does not show an identity matrix.
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