Ciao Orlando,
seguendo il “principio della sequenzialità” (come lo definisco io :D), ecco come puoi fare:
`% TikZ
\usepackage{tikz}
% Librerie
\usetikzlibrary{automata}
\usetikzlibrary{arrows}
\usetikzlibrary{backgrounds}
\usetikzlibrary{calc}
\usetikzlibrary{hobby}
\usetikzlibrary{intersections}
\usetikzlibrary{mindmap}
\usetikzlibrary{patterns}
\usetikzlibrary{positioning}
\usetikzlibrary{shadows}
\usetikzlibrary{shapes}
\usetikzlibrary{through}
\usetikzlibrary{trees}
% Pacchetti
\usepackage{tkz-euclide}
\usetkzobj{all}
\begin{tikzpicture}
% definizioni e macro
\def\l{3}
\def\h{5}
\def\xrad{7}
\pgfmathsetmacro{\apx}{\l/3}
\pgfmathsetmacro{\apy}{\h/6}
\pgfmathsetmacro{\yrad}{\h/2-\apy}
\def\dy{1}
\def\xprad{4}
\pgfmathsetmacro{\yprad}{\yrad-\dy}
% coordinate
%rettangolo
\coordinate (a) at (0,0);
\coordinate (b) at ($(a)+(\l,0)$);
\coordinate (c) at ($(a)+(\l,\h)$);
\coordinate (d) at ($(a)+(0,\h)$);
%arco
\coordinate (a') at (\apx,\apy);
% disegno rettangolo
\fill [cyan!55] (a) — (b) — (c) — (d) — cycle;
\draw (a) — (b) — (c) — (d) — cycle;
% disegno arco
\fill [cyan!55] (a') arc [start angle=270, delta angle=180,x radius=\xrad, y radius=\yrad] — ++(0,-\dy) arc [start angle=90, delta angle=-180,x radius=\xprad, y radius=\yprad] — cycle;
\draw (a') arc [start angle=270, delta angle=180,x radius=\xrad, y radius=\yrad] — ++(0,-\dy) arc [start angle=90, delta angle=-180,x radius=\xprad, y radius=\yprad] — cycle;
\end{tikzpicture}`
Ciao,
Marco.