Chapter 3: Problem 7
Prove that if \(\left(v_{1}, \ldots, v_{n}\right)\) spans \(V\) and \(T \in \mathcal{L}(V, W)\) is surjective, then \(\left(T v_{1}, \ldots, T v_{n}\right)\) spans \(W\).
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Chapter 3: Problem 7
Prove that if \(\left(v_{1}, \ldots, v_{n}\right)\) spans \(V\) and \(T \in \mathcal{L}(V, W)\) is surjective, then \(\left(T v_{1}, \ldots, T v_{n}\right)\) spans \(W\).
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Suppose that \(V\) and \(W\) are finite dimensional and that \(U\) is a subspace of \(V .\) Prove that there exists \(T \in \mathcal{L}(V, W)\) such that null \(T=U\) if and only if \(\operatorname{dim} U \geq \operatorname{dim} V-\operatorname{dim} W\)
Suppose that \(V\) is finite dimensional and \(T \in \mathcal{L}(V) .\) Prove that \(T\) is a scalar multiple of the identity if and only if \(S T=T S\) for every \(S \in \mathcal{L}(V)\)
Give an example of a function \(f: \mathbf{R}^{2} \rightarrow \mathbf{R}\) such that $$f(a v)=a f(v)$$ for all \(a \in \mathbf{R}\) and all \(v \in \mathbf{R}^{2}\) but \(f\) is not linear.
Prove that if \(T\) is a linear map from \(\mathbf{F}^{4}\) to \(\mathbf{F}^{2}\) such that null \(T=\left\\{\left(x_{1}, x_{2}, x_{3}, x_{4}\right) \in \mathbf{F}^{4}: x_{1}=5 x_{2} \text { and } x_{3}=7 x_{4}\right\\}\) then \(T\) is surjective
Prove that every linear map from Mat( \(n, 1, \mathbf{F}\) ) to Mat( \(m, 1, \mathbf{F}\) ) is given by a matrix multiplication. In other words, prove that if \(T \in \mathcal{L}(\operatorname{Mat}(n, 1, \mathbf{F}), \operatorname{Mat}(m, 1, \mathbf{F})),\) then there exists an \(m\) -by- \(n\) matrix \(A\) such that \(T B=A B\) for every \(B \in \operatorname{Mat}(n, 1, \mathbf{F})\)
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