### Background

In my previous post about unit circle and trigonometric functions, I included a graph with three trigonometry functions. I’m quite satisfied with my TikZ picture.

### Problem

Unluckily, a secondary school student found that my diagram was too complicated.

### Solution

```
\documentclass[tikz,border=2pt]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.18}
\usetikzlibrary{calc}
\newcommand\mytheta{110} %angle theta
\begin{document}
\begin{tikzpicture}[scale=2]
\coordinate[label=left:$O$] (O) at (0,0);
\coordinate[label=above left:${A = (\cos\theta, \sin\theta)}$] (A) at (\mytheta:1);
\coordinate[label=below left:${B = (\cos(-\theta), \sin(-\theta))}$] (B) at (-\mytheta:1);
\coordinate[label=right:$E$] (E) at (1,0);
\draw (O) circle (1);
\draw (A) -- (O) node [midway, left] {$1$}
-- (E);
\draw (B) -- (O);
\draw[-stealth] ($(O)!0.3!(E)$) arc (0:\mytheta:0.3) node[midway, above] {$\theta$};
\draw[-stealth] ($(O)!0.25!(E)$) arc (0:{-\mytheta}:0.25) node[midway, below] {$-\theta$};
\end{tikzpicture}
\end{document}
```

Skills learnt:

`\coordinate[label=above left:$O$] (O) at (0,0);`

for labelling a point.- Inside the
`$...$`

, if I put`A = (\cos \theta, \sin \theta)`

, the system will complain. We have to surround this with a pair of curly braces`${...}$`

. - To produce the convex combination of two points
`($(O)!.3!(E)$)`

, we have to wrap the whole expression with a pair of parenthesis.