Let a be a nonzero vector in \( \mathbb{R}^{2} \). Define \( \tau_{\mathbf{a}}: \mathbb{R}^{2} \rightarrow \mathbb{R}^{2} \) by \[ \tau_{\mathbf{a}}(\mathbf{x})=-\mathbf{x}+2 \frac{\mathbf{a} \cdot \mathbf{x}}{\mathbf{a} \cdot \mathbf{a}} \mathbf{a} \] 2. Let a be a nonzero vector of \( \mathbb{R}^{2} \). Answer the following questions. (iii) Find the matrix \( \left[\tau_{\mathbf{a}}\right]_{\mathcal{B}}^{\mathcal{B}} \) of \( \tau_{\mathbf{a}} \) with respect to \( \mathcal{B} \) and \( \mathcal{B} \).
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To find the matrix \( \left[\tau_{\mathbf{a}}\right]_{\mathcal{B}}^{\mathcal{B}} \) for the transformation \( \tau_{\mathbf{a}} \), we proceed with the following steps: ### Step 1: Define the Vector \( \mathbf{a} \) and the Basis \( \mathcal{B} \) Let \( \mathbf{a} = \begin{pmatrix} a_1 \\ a_2 \end{pmatrix} \) be a nonzero vector in \( \mathbb{R}^2 \). Suppose our basis \( \mathcal{B} \) consists of the standard basis vectors: \[ \mathcal{B} = \left\{ \begin{pmatrix} 1 \\ 0 \end{pmatrix}, \begin{pmatrix} 0 \\ 1 \end{pmatrix} \right\} \] ### Step 2: Compute \( \tau_{\mathbf{a}} \) on Basis Vectors Next, we apply \( \tau_{\mathbf{a}} \) on the basis vectors: 1. For \( \mathbf{x}_1 = \begin{pmatrix} 1 \\ 0 \end{pmatrix} \): \[ \tau_{\mathbf{a}}(\mathbf{x}_1) = -\begin{pmatrix} 1 \\ 0 \end{pmatrix} + 2 \frac{\mathbf{a} \cdot \begin{pmatrix} 1 \\ 0 \end{pmatrix}}{\mathbf{a} \cdot \mathbf{a}} \mathbf{a} \] The dot product \( \mathbf{a} \cdot \begin{pmatrix} 1 \\ 0 \end{pmatrix} = a_1 \) and \( \mathbf{a} \cdot \mathbf{a} = a_1^2 + a_2^2 \). Thus, \[ \tau_{\mathbf{a}}(\mathbf{x}_1) = -\begin{pmatrix} 1 \\ 0 \end{pmatrix} + 2 \cdot \frac{a_1}{a_1^2 + a_2^2} \begin{pmatrix} a_1 \\ a_2 \end{pmatrix} = \begin{pmatrix} -1 + \frac{2a_1^2}{a_1^2 + a_2^2} \\ \frac{2a_1a_2}{a_1^2 + a_2^2} \end{pmatrix} \] 2. For \( \mathbf{x}_2 = \begin{pmatrix} 0 \\ 1 \end{pmatrix} \): \[ \tau_{\mathbf{a}}(\mathbf{x}_2) = -\begin{pmatrix} 0 \\ 1 \end{pmatrix} + 2 \frac{\mathbf{a} \cdot \begin{pmatrix} 0 \\ 1 \end{pmatrix}}{\mathbf{a} \cdot \mathbf{a}} \mathbf{a} \] The dot product \( \mathbf{a} \cdot \begin{pmatrix} 0 \\ 1 \end{pmatrix} = a_2 \). Thus, \[ \tau_{\mathbf{a}}(\mathbf{x}_2) = -\begin{pmatrix} 0 \\ 1 \end{pmatrix} + 2 \cdot \frac{a_2}{a_1^2 + a_2^2} \begin{pmatrix} a_1 \\ a_2 \end{pmatrix} = \begin{pmatrix} \frac{2a_1a_2}{a_1^2 + a_2^2} \\ -1 + \frac{2a_2^2}{a_1^2 + a_2^2} \end{pmatrix} \] ### Step 3: Construct the Matrix The resulting vectors from applying \( \tau_{\mathbf{a}} \) to the basis vectors are now: \[ \tau_{\mathbf{a}}(\mathbf{x}_1) = \begin{pmatrix} -1 + \frac{2a_1^2}{a_1^2 + a_2^2} \\ \frac{2a_1a_2}{a_1^2 + a_2^2} \end{pmatrix}, \quad \tau_{\mathbf{a}}(\mathbf{x}_2) = \begin{pmatrix} \frac{2a_