Find the standard matrix for each linear transformation. Give on.

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
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### Linear Transformations and Their Standard Matrices

In this section, we will find the standard matrix for each given linear transformation and provide some explanations for better understanding.

#### Problem 2:

**Find the standard matrix for each linear transformation. Give some explanation.**

---

**a.** \( T : \mathbb{R}^2 \to \mathbb{R}^2 \) *rotates points about the origin by 180° (or \(\pi\) radians).*

**Explanation:**
The standard matrix for a rotation by \( \theta \) around the origin is given by:
\[ \begin{pmatrix}
\cos(\theta) & -\sin(\theta) \\
\sin(\theta) & \cos(\theta)
\end{pmatrix} \]

For a rotation by 180° or \(\pi\) radians:
\[ \cos(\pi) = -1 \]
\[ \sin(\pi) = 0 \]

Therefore, the standard matrix for this transformation is:
\[ \begin{pmatrix}
-1 & 0 \\
0 & -1
\end{pmatrix} \]

---

**b.** \( T : \mathbb{R}^2 \to \mathbb{R}^2 \) *reflects points about the line \( y = -x \).*

**Explanation:**
The reflection matrix about the line \( y = -x \) can be derived using the formula for reflection across a line \( y = mx \):
\[ \begin{pmatrix}
\frac{1-m^2}{1+m^2} & \frac{2m}{1+m^2} \\
\frac{2m}{1+m^2} & \frac{m^2-1}{1+m^2}
\end{pmatrix} \]

For \( y = -x \), the slope \( m \) is -1:
\[ \begin{pmatrix}
\frac{1-(-1)^2}{1+(-1)^2} & \frac{2(-1)}{1+(-1)^2} \\
\frac{2(-1)}{1+(-1)^2} & \frac{(-1)^2-1}{1+(-1)^2}
\end{pmatrix} = \begin{pmatrix}
0 & -1 \\
-1 &
Transcribed Image Text:### Linear Transformations and Their Standard Matrices In this section, we will find the standard matrix for each given linear transformation and provide some explanations for better understanding. #### Problem 2: **Find the standard matrix for each linear transformation. Give some explanation.** --- **a.** \( T : \mathbb{R}^2 \to \mathbb{R}^2 \) *rotates points about the origin by 180° (or \(\pi\) radians).* **Explanation:** The standard matrix for a rotation by \( \theta \) around the origin is given by: \[ \begin{pmatrix} \cos(\theta) & -\sin(\theta) \\ \sin(\theta) & \cos(\theta) \end{pmatrix} \] For a rotation by 180° or \(\pi\) radians: \[ \cos(\pi) = -1 \] \[ \sin(\pi) = 0 \] Therefore, the standard matrix for this transformation is: \[ \begin{pmatrix} -1 & 0 \\ 0 & -1 \end{pmatrix} \] --- **b.** \( T : \mathbb{R}^2 \to \mathbb{R}^2 \) *reflects points about the line \( y = -x \).* **Explanation:** The reflection matrix about the line \( y = -x \) can be derived using the formula for reflection across a line \( y = mx \): \[ \begin{pmatrix} \frac{1-m^2}{1+m^2} & \frac{2m}{1+m^2} \\ \frac{2m}{1+m^2} & \frac{m^2-1}{1+m^2} \end{pmatrix} \] For \( y = -x \), the slope \( m \) is -1: \[ \begin{pmatrix} \frac{1-(-1)^2}{1+(-1)^2} & \frac{2(-1)}{1+(-1)^2} \\ \frac{2(-1)}{1+(-1)^2} & \frac{(-1)^2-1}{1+(-1)^2} \end{pmatrix} = \begin{pmatrix} 0 & -1 \\ -1 &
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