Question
True or false: If $\mathbf{v}_1, \mathbf{v}_2, \mathbf{v}_3$ are a basis for $\mathbb{R}^3$, then they form an orthogonal basis under some appropriately weighted inner product $\langle\mathbf{v}, \mathbf{w}\rangle=a v_1 w_1+b v_2 w_2+c v_3 w_3$.
Step 1
We are given three vectors $\mathbf{v}_1, \mathbf{v}_2, \mathbf{v}_3$ that form a basis for $\mathbb{R}^3$. This means that these vectors are linearly independent and span $\mathbb{R}^3$. We need to determine if they can form an orthogonal basis under some Show more…
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Key Concepts
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In Exercises 17 and $18,$ all vectors and subspaces are in $\mathbb{R}^{n} .$ Mark each statement True or False. Justify each answer. a. If $\left\{\mathbf{v}_{1}, \mathbf{v}_{2}, \mathbf{v}_{3}\right\}$ is an orthogonal basis for $W,$ then mul- tiplying $\mathbf{v}_{3}$ by a scalar $c$ gives a new orthogonal basis $\left\{\mathbf{v}_{1}, \mathbf{v}_{2}, c \mathbf{v}_{3}\right\} .$ b. The Gram-Schmidt process produces from a linearly in- dependent set $\left\{\mathbf{x}_{1}, \ldots, \mathbf{x}_{p}\right\}$ an orthogonal set $\left\{\mathbf{v}_{1}, \ldots, \mathbf{v}_{p}\right\}$ with the property that for each $k,$ the vectors $\mathbf{v}_{1}, \ldots, \mathbf{v}_{k}$ span the same subspace as that spanned by $\mathbf{x}_{1}, \ldots, \mathbf{x}_{k}$ c. If $A=Q R,$ where $Q$ has orthonormal columns, then $R=Q^{T} A$
Orthogonality and Least Square
The Gram–Schmidt Process
Show that $\left\{\mathbf{u}_{1}, \mathbf{u}_{2}\right\}$ or $\left\{\mathbf{u}_{1}, \mathbf{u}_{2}, \mathbf{u}_{3}\right\}$ is an orthogonal basis for $\mathbb{R}^{2}$ or $\mathbb{R}^{3},$ respectively. Then express $\mathbf{x}$ as a linear combination of the $\mathbf{u}^{\prime}$s. $\mathbf{u}_{1}=\left[\begin{array}{r}{3} \\ {-3} \\ {0}\end{array}\right], \mathbf{u}_{2}=\left[\begin{array}{r}{2} \\ {2} \\ {-1}\end{array}\right], \mathbf{u}_{3}=\left[\begin{array}{l}{1} \\ {1} \\ {4}\end{array}\right],$ and $\mathbf{x}=\left[\begin{array}{r}{5} \\ {-3} \\ {1}\end{array}\right]$
Orthogonal Sets
True or false (give an example in either case): (a) $Q^{-1}$ is an orthogonal matrix when $Q$ is an orthogonal matrix. (b) If $Q$ ( 3 by 2$)$ has orthonormal columns then $\|Q x\|$ always equals $\|x\|$.
Orthogonality
Orthogonal Bases and Gram-Schmidt
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