最近整左個 file 作為 micro taching 嘅 ``material" (其實都係做樣，有人睇先算)。
http://ihome.ust.hk/~cclee/document/microteaching.pdf
咁 present 時當然唔可以用 d 咁 dense 嘅野...，我求求其其將佢 extract 左做 slide
http://ihome.ust.hk/~cclee/document/testbeamer.pdf
當中所有圖都係 tikz 畫，真係好 Q 麻煩，不過幾煩都好，都係熟能生巧...。其中我 define 左兩個 command 幾好用，留喺呢個 blog 等自己想搵返先都方便 d。
畫兩條線之間嘅 arc about 某一點：
#1 = pt, #2 = from which angle, #3 = to which angle, #4 = radius
\newcommand{\arc}[4]{#1 + (#2:#4) arc (#2:#3:#4)}
至於畫直角：
#1 about which point:
#2: angle of diagonal point
#3 length of diagonal line
\newcommand{\rightangle}[3]{
\begin{scope}[shift={#1}]
\coordinate (the point u draw angle) at (0,0);
\coordinate (diagonal point) at (#2:#3);
\coordinate (one side) at ($(the point u draw angle)!0.707106781186!45:(diagonal point)$);
\coordinate (another side) at ($(the point u draw angle)!0.707106781186!-45:(diagonal point)$);
\draw(one side) -- (diagonal point)--(another side);
\end{scope}
}
實際上冇可能下下都好準確咁計哂 d angle 出黎 (太花時間)，所以好多時都係靠估，然後睇下 match 唔 match。
