Chapter 1: Problem 10
Suppose that \(U\) is a subspace of \(V\). What is \(U+U ?\)
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Chapter 1: Problem 10
Suppose that \(U\) is a subspace of \(V\). What is \(U+U ?\)
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Give an example of a nonempty subset \(U\) of \(R^{2}\) such that \(U\) is closed under addition and under taking additive inverses (meaning \(-u \in U\) whenever \(u \in U\) ), but \(U\) is not a subspace of \(\mathbf{R}^{2}.\)
Suppose \(a\) and \(b\) are real numbers, not both 0. Find real numbers \(c\) and \(d\) such that \\[ 1 /(a+b i)=c+d i \\]
Prove that the intersection of any collection of subspaces of \(V\) is a subspace of \(V\)
Prove that if \(a \in \mathbf{F}, v \in V,\) and \(a v=0,\) then \(a=0\) or \(v=0\)
Prove or give a counterexample: if \(U_{1}, U_{2}, W\) are subspaces of \(V\) such that \\[ U_{1}+W=U_{2}+W \\] \(\operatorname{then} U_{1}=U_{2}\)
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