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2023-04-16 17:29:46 -07:00
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commit 4e33edf6e7
4 changed files with 357 additions and 90 deletions

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@ -9,7 +9,16 @@
%\usepackage{lua-visual-debug}
\usepackage{tikz-3dplot}
\usetikzlibrary{quotes,angles}
\usetikzlibrary{
quotes,
angles,
matrix,
decorations.pathreplacing,
calc,
positioning,
fit
}
\input{tikzset}
\begin{document}
@ -24,97 +33,10 @@
\input{parts/0 notation}
\input{parts/1 vectors}
\section{Dot Products}
\definition{}
We can also define the \textit{dot product} of two vectors.\footnotemark{} \\
The dot product maps two elements of $\mathbb{R}^n$ to one element of $\mathbb{R}$:
\footnotetext{
\textbf{Bonus content. Feel free to skip.}
Formally, we would say that the dot product is a map from $\mathbb{R}^n \times \mathbb{R}^n$ to $\mathbb{R}$. Why is this reasonable?
\vspace{2mm}
It's also worth noting that a function $f$ from $X$ to $Y$ can defined as a subset of $X \times Y$, where for all $x \in X$ there exists a unique $y \in Y$ so that $(x, y) \in f$. Try to make sense of this definition.
}
$$
a \cdot b = \sum_{i = 1}^n a_ib_i = a_1b_1 + a_2b_2 + ... + a_nb_n
$$
\problem{}
Compute $[2, 3, 4, 1] \cdot [2, 4, 10, 12]$
\vfill
\problem{}
Show that the dot product is
\begin{itemize}
\item Commutative
\item Distributive
\item Homogeneic: $x(a \cdot b) = xa \cdot b = a \cdot xb$
\item Positive definite: $a \cdot a \geq 0$, with equality iff $a = 0$
\end{itemize}
\input{parts/2 dotprod}
\input{parts/3 matrices}
\vfill
\pagebreak
\problem{}
Say you have two vectors, $a$ and $b$. Show that $\langle a, b \rangle$ = $||a||~||b||\cos(\alpha)$ \\
\hint{What is $c$ in terms of $a$ and $b$?}
\hint{The law of cosines is $a^2 + b^2 - 2ab\cos(\alpha) = c^2$}
\hint{The length of $a$ is $||a||$}
\begin{center}
\begin{tikzpicture}[scale=1]
\draw[->]
(0,0) coordinate (o) -- node[above left] {$a$}
(1,2) coordinate (a)
;
\draw[->]
(o) -- node[below] {$b$}
(3,0.5) coordinate (b)
;
\draw[
draw = gray,
text = gray,
-
] (a) -- node[above] {$c$} (b);
\draw
pic[
"$\alpha$",
draw = orange,
text = orange,
<->,
angle eccentricity = 1.2,
angle radius = 1cm
]
{ angle = b--o--a }
;
\end{tikzpicture}
\end{center}
\vfill
\problem{}
If $a$ and $b$ are perpendicular, what must $\langle a, b \rangle$ be? Is the converse true?
\vfill
\pagebreak
\section{Bonus}