00:05 – 共圓點的概念 | concepts of concyclic points03:59 – 測試共圓點 | tests for concyclic points07:02 – 反證法的概念 | concepts of proof by contradiction11:32 – 例子 1 | example 112:45 – 例子 2 | example 216:12 – 例子 3 | example 3