有向數加減運算 | Addition and Subtraction of Directed Numbers
影片內容：
00:25 – 正數加減 | adding / subtracting positive numbers
03:33 – 負數加減 | adding / subtracting negative numbers
08:32 – 例子 | example
00:25 – 正數加減 | adding / subtracting positive numbers
03:33 – 負數加減 | adding / subtracting negative numbers
08:32 – 例子 | example