Lorentz
I am trying to draw this picture
I tried
```
\documentclass[border=5mm]{standalone}
\usepackage{tkz-euclide}
\begin{document}
\begin{tikzpicture}[declare function={r=1;myangle=30;},c/.style={circle,fill,inner sep=1pt},>=latex,scale=2]
\path
(0,0) coordinate (O)
(myangle:r) coordinate (M)
(180-myangle:r) coordinate (M')
;
\draw[->] (-1.5,0) -- (1.5,0) node[below] {$x$};
\draw[->] (0,-1.5) -- (0,1.5) node[right] {$y$};
% draw the unit circle
\draw[thick] (0,0) circle[radius=1];
\draw[dashed]
(M') -- (M) ;
\draw (0,0) -- (M) (0,0) -- (M');
\path foreach \p/\g in {O/-45,M/90,M'/90}{(\p)node[c]{}+(\g:1.8mm) node{$\p$}};
\end{tikzpicture}
\end{document}
```
I get
Top Answer
frougon
I propose the following that uses:
- the `-|` binary operator to compute coordinates;
- the `angles` Ti*k*Z library for angle markings, and;
- the `quotes` Ti*k*Z library for convenience.
I removed the `scale=2` setting because it would make the circle `radius` and the `angle radius` of the angle markings inconsistent (the latter wouldn't be scaled). Of course, I adapted the coordinates accordingly.
I also colored the 𝛼 angle label in the same color (blue) as the corresponding arrow for clarity.
```
\documentclass[tikz,border=2mm]{standalone}
\usetikzlibrary{angles, quotes}
\begin{document}
\begin{tikzpicture}[
declare function={r=2cm; myangle=30; ax=1.3*r;},
c/.style={circle, fill, inner sep=1pt},
>=latex,
]
\path (0,0) coordinate (O)
(myangle:r) coordinate (M)
(180-myangle:r) coordinate (M')
(O -| M') coordinate (K)
(O -| M) coordinate (H);
\draw[->] (-ax,0) -- (ax,0) node[below] {$x$};
\draw[->] (0,-ax) -- (0,ax) node[right] {$y$};
% The unit circle
\draw[thick] (0,0) circle[radius=r];
\draw[dashed] (K) -- (M') -- (M) -- (H);
\draw (M') -- (O) -- (M);
\path foreach \p/\g in {O/-45, M/45, M'/135, K/-90, H/-90} {
(\p) node[c] {} +(\g:0.15*r) node{$\p$}
};
% The angle arrows and labels
\draw[->]
pic ["$\alpha$" blue, draw=blue, angle radius=0.25*r,
angle eccentricity=1.4] {angle = H--O--M}
pic ["$\pi - \alpha$", draw, angle radius=0.46*r,
angle eccentricity=0.68] {angle = H--O--M'};
\end{tikzpicture}
\end{document}
```
