TikZ: two figures corresponding to each other

Question

Now I have not yet started making this picture, and I would like some pointers. Any method to produce the image is sufficient, alas I would prefer TikZ and perhaps tkz-euclide over asympote or similar

A rope is 10 meters long. We cut the rope in half, where the first part is made into a equilateral triangle and the second part is made into a square.

The part that is used for the triangle is x meters long.

What my problem is, is that I do not know how to change the size of the square accordingly to the triangle.

For example if I say that 2 meters goes to the triangle. How would I make TikZ know that 8 would go to the square?

Answer 1

\documentclass{scrartcl}   
\usepackage{tkz-euclide}
\usetkzobj{all}    
\begin{document}

\def\totallength{10}  

\foreach \len in {2,5,8} 
{%    
  \begin{tikzpicture}
    \tkzDefPoint(0,0){A};
    \tkzDefPoint(\len/3,0){B};  
    \tkzDefShiftPoint[B](0.5,0){C}; 
    \tkzDefShiftPoint[C](\totallength/4-\len/4,0){D}; 
    \tkzDrawTriangle[equilateral](A,B)   
    \tkzDrawSquare(C,D) 
 \end{tikzpicture}\par}

\end{document}  

Answer 2

\pgfmathsetmacro is your friend:

\documentclass[parskip]{scrartcl}
\usepackage[margin=15mm]{geometry}
\usepackage{tikz}

\begin{document}

\pgfmathsetmacro{\totallength}{10}

\begin{tikzpicture}
% --- only edit the next ---
\pgfmathsetmacro{\trianglelength}{2}
% --- --- --- --- --- --- --- ---
\pgfmathsetmacro{\triangleside}{\trianglelength/3}
\pgfmathsetmacro{\squarelength}{\totallength-\trianglelength}
\pgfmathsetmacro{\squareside}{\squarelength/4}
\draw (-0.1,0) -- ++(180:\triangleside) -- ++(60:\triangleside) -- cycle;
\draw (0.1,0) rectangle ++(\squareside,\squareside);
\end{tikzpicture}

\begin{tikzpicture}
% --- only edit the next ---
\pgfmathsetmacro{\trianglelength}{5}
% --- --- --- --- --- --- --- ---
\pgfmathsetmacro{\triangleside}{\trianglelength/3}
\pgfmathsetmacro{\squarelength}{\totallength-\trianglelength}
\pgfmathsetmacro{\squareside}{\squarelength/4}
\draw (-0.1,0) -- ++(180:\triangleside) -- ++(60:\triangleside) -- cycle;
\draw (0.1,0) rectangle ++(\squareside,\squareside);
\end{tikzpicture}

\begin{tikzpicture}
% --- only edit the next ---
\pgfmathsetmacro{\trianglelength}{8}
% --- --- --- --- --- --- --- ---
\pgfmathsetmacro{\triangleside}{\trianglelength/3}
\pgfmathsetmacro{\squarelength}{\totallength-\trianglelength}
\pgfmathsetmacro{\squareside}{\squarelength/4}
\draw (-0.1,0) -- ++(180:\triangleside) -- ++(60:\triangleside) -- cycle;
\draw (0.1,0) rectangle ++(\squareside,\squareside);
\end{tikzpicture}

\end{document}