Differential Equations and Linear Algebra (4th Edition)

Published by Pearson
ISBN 10: 0-32196-467-5
ISBN 13: 978-0-32196-467-0

Chapter 6 - Linear Transformations - 6.2 Transformations of R2 - Problems - Page 397: 14

Answer

See below

Work Step by Step

Given: $A=\begin{bmatrix} \cos \theta & -\sin \theta\\ \sin \theta& \cos \theta \end{bmatrix}$ Let's reduce $A$ to the row-echelon form $\begin{bmatrix} \cos \theta & -\sin \theta\\ \sin \theta& \cos \theta \end{bmatrix}\approx \begin{bmatrix} 1 & -\tan \theta\\ \sin \theta& \cos \theta \end{bmatrix} \approx \begin{bmatrix} 1 & -\tan \theta\\ 0&\frac{1}{ \cos \theta} \end{bmatrix}\approx \begin{bmatrix} 1 & -\tan \theta\\ 0 & 1 \end{bmatrix} \approx \begin{bmatrix} 1 & 0\\ 0 & 1 \end{bmatrix}$ where $1.M_1(\frac{1}{\cos \theta}) \\ 2.M_2(-\sin \theta)\\ 3. M_2(\cos \theta)\\ 4.A_{12}(\tan \theta)$ Thus, $T(x)=Ax=M_1(\cos \theta)A_{12}(\sin \theta)M_2(\frac{1}{\cos \theta})A_{12}(-\tan \theta)x$ For $\theta \in [<0,\frac{\pi}{2}>\cup ]\rightarrow \cos \theta \gt 0$ and $\frac{1}{\cos \theta} \gt 0$, $A$ is a product of a shear parallel to the y-axis followed by a linear stretch in the y direction, followed by a shear parallel to the x-axis, followed by a linear stretch in the x-direction. For $\theta \in [\rightarrow \cos \theta \lt 0$ and $\frac{1}{\cos \theta} \lt 0$, $A$ is a product of a shear parallel to the y-axis followed by a reflection in the x axis followed by a linear stretch in the y direction, followed by a shear parallel in the x-axis, followed by a reflection in the y-axis followed by a linear stretch in the x-direction.
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