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Screwdriver
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Homework Statement
Let [tex]\vec{u}\neq 0[/tex] be a vector in [tex]\mathbb{R}^2[/tex] and let
[tex]T:\mathbb{R}^2 \to \mathbb{R}^2[/tex] be described by
[tex]T:\vec{v} \to proj_{\vec{u}}(\vec{v})[/tex]
If [tex]\vec{u}=[1,-1][/tex]
Find the standard matrix for [tex]T[/tex]
Homework Equations
[tex]proj_{\vec{u}}(\vec{v})= \frac{\vec{v}\cdot\vec{u} }{\vec{u}\cdot\vec{u}}\vec{u}[/tex]
The Attempt at a Solution
Determine where [tex]T[/tex] sends [tex]\vec{e_1}[/tex] and [tex]\vec{e_2}[/tex]
[tex]f(\vec{e_1})= \frac{\vec{e_1}\cdot\vec{u} }{\vec{u}\cdot\vec{u}}\vec{u}[/tex]
[tex]f(\vec{e_1})= \frac{[1,0]\cdot [1,-1]}{[1,-1]\cdot [1,-1]}[/tex]
[tex]f(\vec{e_1})= [\frac{1}{2},-\frac{1}{2}][/tex]
[tex]f(\vec{e_2})= \frac{\vec{e_2}\cdot\vec{u} }{\vec{u}\cdot\vec{u}}\vec{u}[/tex]
[tex]f(\vec{e_2})= \frac{[0,1]\cdot [1,-1]}{[1,-1]\cdot [1,-1]}[/tex]
[tex]f(\vec{e_2})= [-\frac{1}{2},\frac{1}{2}][/tex]
So does that mean that the standard matrix is
[tex]
\begin{bmatrix}
\frac{1}{2} & -\frac{1}{2} \\
-\frac{1}{2} & \frac{1}{2} \\
\end{bmatrix}
[/tex]
?
[Edited twice for LaTex mistakes]
Last edited: