Chapter 5: Problem 11
Prove that the transpose of an orthogonal matrix is an orthogonal matrix.
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Chapter 5: Problem 11
Prove that the transpose of an orthogonal matrix is an orthogonal matrix.
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Let \(U\) and \(V\) be subspaces of a vector space \(W\) Show that if \(W=U \oplus V,\) then \(U \cap V=\\{0\\}\)
Prove: If \(A\) is an \(m \times n\) matrix and \(\mathbf{x} \in \mathbb{R}^{n},\) then cither \(A \mathbf{x}=0\) or there exists \(\mathbf{y} \in R\left(A^{T}\right)\) such that \(\mathbf{x}^{T} \mathbf{y} \neq 0 .\) Draw a picture similar to Figure 5.2 .2 to illustrate this result geometrically for the case where \(N(A)\) is a two-dimensional subspace of \(\mathbb{R}^{3}\)
Let \(\mathbf{x}\) and \(\mathbf{y}\) be vectors in \(\mathbb{R}^{n}\) and define $$\mathbf{p}=\frac{\mathbf{x}^{T} \mathbf{y}}{\mathbf{y}^{T} \mathbf{y}} \mathbf{y} \quad \text { and } \quad \mathbf{z}=\mathbf{x}-\mathbf{p}$$ (a) Show that \(\mathbf{p} \perp\) z. Thus, \(\mathbf{p}\) is the vector projection of \(\mathbf{x}\) onto \(\mathbf{y} ;\) that is, \(\mathbf{x}=\mathbf{p}+\mathbf{z},\) where \(\mathbf{p}\) and \(\mathbf{z}\) are orthogonal components of \(\mathbf{x},\) and \(\mathbf{p}\) is a scalar multiple of \(\mathbf{y}\) (b) If \(\|\mathbf{p}\|=6\) and \(\|\mathbf{z}\|=8,\) determine the value of \(\|\mathbf{x}\|\)
If \(V\) is an inner product space, show that $$\|\mathbf{v}\|=\sqrt{\langle\mathbf{v}, \mathbf{v}\rangle}$$ satisfies the first two conditions in the definition of a norm.
Show that, for any \(\mathbf{u}\) and \(\mathbf{v}\) in a normed vector space, $$\|\mathbf{u}+\mathbf{v}\| \geq |\|\mathbf{u}\|-\|\mathbf{v}\|$$
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