# Example: Circles in and around a triangle

Published 2015-09-24 | Author: Stefan Kottwitz

Here we see how easy it is to define circles tangential or by peripheral points.

• we define objects
• then we refere to them
• we chose an order, so later drawn objects overwrite earlier drawn objects

The code is a follow-up to the Releux triangle recipe.

It is explained in the LaTeX Cookbook, Chapter 10, Advanced Mathematics, Drawing geometry pictures.

Download as: [PDF] [TEX]  •  [Open in Overleaf]

% Circles in and around a triangle
% Author: Stefan Kottwitz
% https://www.packtpub.com/hardware-and-creative/latex-cookbook
\documentclass[border=10pt]{standalone}
\usepackage{tkz-euclide}
\usetkzobj{all}
\begin{document}
\begin{tikzpicture}
\tkzDefPoints{0/0/A, 5/0/B, 1/4/C}
\tkzDefCircle[in](A,B,C)
\tkzGetPoint{M}
\tkzGetLength{r}
\tkzDefCircle[circum](A,B,C)
\tkzGetPoint{N}
\tkzGetLength{R}
\tkzDefPointBy[projection=onto A--B](M)
\tkzGetPoint{a}
\tkzDefPointBy[projection=onto B--C](M)
\tkzGetPoint{b}
\tkzDefPointBy[projection=onto A--C](M)
\tkzGetPoint{c}

\tkzDrawCircle[R](M,\r pt)
\tkzDrawCircle[R](N,\R pt)
\tkzDrawPolygon[very thick](A,B,C)
\tkzDrawLines[dotted](N,A N,B N,C)
\tkzDrawLines[dashed](M,a M,b M,c)
\tkzMarkRightAngles(M,a,B M,b,C M,c,C)
\tkzDrawPoints(A,B,C,M,N,a,b,c)
\tkzLabelPoints[below left](A,M,a,c)
\tkzLabelPoints[below right](B)
\tkzLabelPoints[above](C,b)
\tkzLabelPoints[below](N)
\end{tikzpicture}
\end{document} 