10.E: Exercises for Chapter 10
- Page ID
- 249
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Calculational Exercises
1. Consider \(\mathbb{R}^3 \) with two orthonormal bases: the canonical basis \(e = (e_1 , e_2 , e_3 )\) and the basis \(f = (f_1 , f_2 , f_3)\), where
\[ f_1 = \frac{1}{\sqrt{3}}(1,1,1), f_2 = \frac{1}{\sqrt{6}}(1,-2,1), f_3 = \frac{1}{\sqrt{2}}(1,0,-1) \]
Find the matrix, \(S\), of the change of basis transformation such that
\[ [v]_f = S[v]_e, ~\rm{for~ all}~ v \in \mathbb{R}^3 ,\]
where \([v]_b\) denotes the column vector of \(v\) with respect to the basis \(b\).
2. Let \(v \in \mathbb{C}^4\) be the vector given by \(v = (1, i, −1, −i)\). Find the matrix (with respect to the canonical basis on \(\mathbb{C}^4\) ) of the orthogonal projection \(P \in \cal{L}(\mathbb{C}^4)\) such that
\[null(P ) = {v}^\perp.\]
3. Let \(U\) be the subspace of \(\mathbb{R}^3\) that coincides with the plane through the origin that is perpendicular to the vector \(n = (1, 1, 1) \in \mathbb{R}^3.\)
(a) Find an orthonormal basis for \(U\).
(b) Find the matrix (with respect to the canonical basis on \(\mathbb{R}^3\)) of the orthogonal projection \(P \in \cal{L}(\mathbb{R}^3\)) onto \(U\), i.e., such that \(range(P ) = U\).
4. Let \(V = \mathbb{C}^4\) with its standard inner product. For \( \theta \in \mathbb{R}\), let
\[ v_\theta = \left( \begin{array}{c} 1 \\ e^{i\theta} \\ e^{2i\theta} \\ e^{3i\theta} \end{array} \right) \in \mathbb{C}^4.\]
Find the canonical matrix of the orthogonal projection onto the subspace \({v_\theta }^\perp\).
Proof-Writing Exercises
1. Let \(V\) be a finite-dimensional vector space over \(\mathbb{F}\) with dimension \(n \in \mathbb{Z}_+ \), and suppose that \(b = (v_1 , v_2 , \ldots , v_n) \) is a basis for \(V\) . Prove that the coordinate vectors \([v_1 ]_b, [v_2 ]_b, \ldots, [v_n ]_b\) with respect to \(b\) form a basis for \(\mathbb{F}^n.\)
2. Let \(V\) be a finite-dimensional vector space over \(\mathbb{F}\), and suppose that \(T \in \cal{L}(V)\) is a linear operator having the following property: Given any two bases \(b\) and \(c\) for \(V\) , the matrix \(M(T, b)\) for \(T\) with respect to \(b\) is the same as the matrix \(M(T, c)\) for \(T\) with respect to \(c\). Prove that there exists a scalar \(\alpha \in \mathbb{F}\) such that \(T = \alpha I_V\), where \(I_V\) denotes the identity map on \(V\).
Contributors
- Isaiah Lankham, Mathematics Department at UC Davis
- Bruno Nachtergaele, Mathematics Department at UC Davis
- Anne Schilling, Mathematics Department at UC Davis
Both hardbound and softbound versions of this textbook are available online at WorldScientific.com.