Linear Algebra and Its Applications (5th Edition)

Published by Pearson
ISBN 10: 032198238X
ISBN 13: 978-0-32198-238-4

Chapter 2 - Matrix Algebra - 2.7 Exercises - Page 147: 11

Answer

See explanation

Work Step by Step

Multiply matrices to see final transformation matrix: \[ \begin{array}{l} A_{2} A_{1}=\left[\begin{array}{ccc} \sec \varphi & -\tan \varphi & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 1 \end{array}\right] \cdot\left[\begin{array}{ccc} 1 & 0 & 0 \\ \sin \varphi & \cos \varphi & 0 \\ 0 & 0 & 1 \end{array}\right]= \\ {\left[\begin{array}{cccc} \sec \varphi-\tan \varphi \sin \varphi & -\tan \varphi \cos \varphi & 0 \\ \sin \varphi & 0 & \cos \varphi & 0 \\ 0 & 0 & 1 \end{array}\right]} \end{array} \] Calculate these expressions: \[ \sec \varphi-\tan \varphi \sin \varphi=\frac{1}{\cos \varphi}-\frac{\sin \varphi}{\cos \varphi} \sin \varphi=\frac{1-\sin ^{2} \varphi}{\cos \varphi}=\frac{\cos ^{2} \varphi}{\cos \varphi}=\cos \varphi \] \[ -\tan \varphi \cos \varphi=-\frac{\sin \varphi}{\cos \varphi} \cos \varphi=-\sin \varphi \] Meaning that the last matrix can be written as: \[ \left[\begin{array}{ccc} \cos \varphi & -\sin \varphi & 0 \\ \sin \varphi & \cos \varphi & 0 \\ 0 & 0 & 1 \end{array}\right] \] This matrix represents a rotation in $\mathbb{R}^{2}$ in homogeneous coordinates.
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