The construction of points on the perpendicular bissector of [AB]. It is achieved in an artisanal way, the purpose being to show how to achieve computations with pgf. A much simpler construction can certainly be done with other pgf commands but the idea here is to emphasize the analytical process.

Edit and compile if you like:
% Perpendicular bissector% Author: Hugues Vermeiren\documentclass{minimal}\usepackage{tikz,xifthen}\usepackage[active,tightpage]{preview}\PreviewEnvironment{tikzpicture}\setlength\PreviewBorder{5pt}%\begin{document}\newcounter{index}\setcounter{index}{0}\begin{tikzpicture}[scale=1.0,MyPoints/.style={draw=blue,fill=white,thick},Segments/.style={draw=blue!50!red!70,thick},MyCircles/.style={green!50!blue!50,thin}]% Warning : all this is an artisanal way of computing points% on the perpendicular bissector of [AB]% It could very well be achieved with more powerfull tools...% (package tkz-2d, for example)\clip (-2.5,-2.5) rectangle (7,7.5);\draw[color=gray,step=1.0,dotted] (-2.1,-2.1) grid (6.1,7.1);\draw[->] (-2,0)--(6.5,0) node[right]{$x$};\draw[->] (0,-2)--(0,7) node[above]{$y$};% Feel free to change here coordinates of points A and B\pgfmathparse{-sqrt(2)} \let\Xa\pgfmathresult\pgfmathparse{2} \let\Ya\pgfmathresult\coordinate (A) at (\Xa,\Ya);\pgfmathparse{5} \let\Xb\pgfmathresult\pgfmathparse{13/3} \let\Yb\pgfmathresult\coordinate (B) at (\Xb,\Yb);% Let I be the midpoint of [AB]\pgfmathparse{(\Xb+\Xa)/2} \let\XI\pgfmathresult\pgfmathparse{(\Yb+\Ya)/2} \let\YI\pgfmathresult
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