Chapter 2: Problem 30
$$ \text { Prove that the subspaces }\\{0\\}, V, R(T) \text {, and } N(T) \text { are all } T \text {-invariant. } $$
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Chapter 2: Problem 30
$$ \text { Prove that the subspaces }\\{0\\}, V, R(T) \text {, and } N(T) \text { are all } T \text {-invariant. } $$
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Recall the definition of \(\mathrm{P}(R)\) on page 11. Define $$ \mathrm{T}: \mathrm{P}(R) \rightarrow \mathrm{P}(R) \quad \text { by } \quad \mathrm{T}(f(x))=\int_{0}^{x} f(t) d t . $$ Prove that \(\mathrm{T}\) linear and one-to-one, but not onto.
Let \(\beta=\left\\{v_{1}, v_{2}, \ldots, v_{n}\right\\}\) be a basis for a vector space \(\mathrm{V}\) and \(\mathrm{T}: \mathrm{V} \rightarrow \mathrm{V}\) be a linear transformation. Prove that \([\mathrm{T}]_{\beta}\) is upper triangular if and only if \(\mathrm{T}\left(v_{j}\right) \in \operatorname{span}\left(\left\\{v_{1}, v_{2}, \ldots, v_{j}\right\\}\right)\) for \(j=1,2, \ldots, n\). Visit goo.gl/k9ZrQb for a solution.
Label the following statements as true or false. In each part, \(V\) and \(W\) are finite-dimensional vector spaces (over \(F\) ), and \(\mathrm{T}\) is a function from \(\mathrm{V}\) to \(\mathrm{W}\). (a) If \(\mathrm{T}\) is linear, then \(\mathrm{T}\) preserves sums and scalar products. (b) If \(\mathrm{T}(x+y)=\mathrm{T}(x)+\mathrm{T}(y)\), then \(\mathrm{T}\) is linear. (c) \(\mathrm{T}\) is one-to-one if and only if the only vector \(x\) such that \(\mathrm{T}(x)=0\) is \(x=0\). (d) If \(T\) is linear, then \(T\left(0_{v}\right)=0_{w}\). (e) If \(T\) is linear, then nullity \((T)+\operatorname{rank}(T)=\operatorname{dim}(W)\). (f) If \(\mathrm{T}\) is linear, then \(\mathrm{T}\) carries linearly independent subsets of \(\mathrm{V}\) onto linearly independent subsets of W. (g) If \(\mathrm{T}, \mathrm{U}: \mathrm{V} \rightarrow \mathrm{W}\) are both linear and agree on a basis for \(\mathrm{V}\), then \(T=U\). (h) Given \(x_{1}, x_{2} \in \mathrm{V}\) and \(y_{1}, y_{2} \in \mathrm{W}\), there exists a linear transformation \(\mathrm{T}: \mathrm{V} \rightarrow \mathrm{W}\) such that \(\mathrm{T}\left(x_{1}\right)=y_{1}\) and \(\mathrm{T}\left(x_{2}\right)=y_{2}\). For Exercises 2 through 6, prove that \(\mathrm{T}\) is a linear transformation, and find bases for both \(N(T)\) and \(R(T)\). Then compute the nullity and rank of \(T\), and verify the dimension theorem. Finally, use the appropriate theorems in this section to determine whether \(\mathrm{T}\) is one-to-one or onto.
In \(\mathrm{R}^{2}\), let \(L\) be the line \(y=m x\), where \(m \neq 0\). Find an expression for \(\mathrm{T}(x, y)\), where (a) \(\mathrm{T}\) is the reflection of \(\mathrm{R}^{2}\) about \(L\). (b) \(\mathrm{T}\) is the projection on \(L\) along the line perpendicular to \(L\). (See the definition of projection in the exercises of Section 2.1.)
Let \(\mathrm{T}: \mathrm{V} \rightarrow \mathrm{W}\) be linear, \(b \in \mathrm{W}\), and \(K=\\{x \in \mathrm{V}: \mathrm{T}(x)=b\\}\) be nonempty. Prove that if \(s \in K\), then \(K=\\{s\\}+\mathrm{N}(\mathrm{T})\). (See page 22 for the definition of the sum of subsets.) The following definition is used in Exercises 25-28 and in Exercise 31 . Definition. Let \(\mathrm{V}\) be a vector space and \(\mathrm{W}_{1}\) and \(\mathrm{W}_{2}\) be subspaces of \(\mathrm{V}\) such that \(\mathrm{V}=\mathrm{W}_{1} \oplus \mathrm{W}_{2}\). (Recall the definition of direct sum given on page 22.) The function \(\mathrm{T}: \mathrm{V} \rightarrow \mathrm{V}\) defined by \(\mathrm{T}(x)=x_{1}\) where \(x=x_{1}+x_{2}\) with \(x_{1} \in \mathrm{W}_{1}\) and \(x_{2} \in \mathrm{W}_{2}\), is called the projection of \(\mathrm{V}\) on \(\mathrm{W}_{1}\) or the projection on \(\mathrm{W}_{1}\) along \(\mathrm{W}_{2}\).
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