【003_モーペルテュイ】コマ大数学科

ビリヤードでAの玉を3クッションでBに最短で入れるためにはどうすればよいか。

\begin{tikzpicture}
  % ==階段，放物線，
  % 線を引く
  \fill [color=yellow!50!white,rounded corners=5pt] (-0.5,-0.5) rectangle (6.5,3.5);
  \draw [very thick] (-0.5,-0.5) rectangle (6.5,3.5);
  \fill [color=green!70!white,very thick](0,0) rectangle (6,3);
  \fill [color=red!70!white] (1.5,2) circle (0.25cm) node (2,1)[font=\small,black]{A};
  \fill [red!20!black] ([shift={($(6,3)-(0.2,0.2)$)}]-45:0.3cm) arc [start angle=-45, end angle=135, radius=0.3cm];
  \fill [red!20!black] ([shift={($(0,3)+(0.2,-0.2)$)}]45:0.3cm) arc [start angle=45, end angle=225, radius=0.3cm];
  \fill [red!20!black] ([shift={($(0,0)+(0.2,0.2)$)}]135:0.3cm) arc [start angle=135, end angle=315, radius=0.3cm];
  \fill [red!50!yellow] ([shift={($(6,0)-(0.2,-0.2)$)}]-135:0.3cm) arc [start angle=-135, end angle=45, radius=0.3cm];
  \node at (5.9,0.1)[font=\small,black]{B};
\end{tikzpicture}