Optical illusions, 1/5
\documentclass[tikz,border=10pt]{standalone}\begin{document}% definition of the pieces, just to show that in% both configurations the same ones are used\newcommand{\bluetriangle}[1][]{\draw[fill=blue,#1](0,0)--( 8,0)--( 8,3)--cycle;}\newcommand{\yellowtriangle}[1][]{\draw[fill=yellow,#1](8,3)--(13,3)--(13,5)--cycle;}\newcommand{\redpolygon}[1][]{\draw[fill=red,#1](8,0)--(13,0)--(13,2)--(10,2)--(10,1)--(8,1)--cycle;}\newcommand{\greenpolygon}[1][]{\draw[fill=green,#1](8,1)--(10,1)--(10,2)--(13,2)--(13,3)--(8,3)--cycle;}\begin{tikzpicture}[x=0.5cm,y=0.5cm,thick]% the grid\draw[help lines,step=1] (-1,-1) grid (14,12);% the complete triangle\bluetriangle\yellowtriangle\redpolygon\greenpolygon% the missing square triangle\begin{scope}[yshift=3cm]\bluetriangle [shift={( 5, 2)}]\yellowtriangle[shift={(-8,-3)}]\redpolygon [shift={( 0, 0)}]\greenpolygon [shift={(-3,-1)}]\end{scope}% the solution (uncomment next line and close in)% \draw[very thin,red] (0,0)--(13,5) {[yshift=3cm] (0,0)--(13,5)};\end{tikzpicture}\end{document}