垂直平分線及外心 | Perpendicular Bisectors and Circumcentre

影片內容：

00:05 – 咩係外心? | what is circumcenter?
01:14 – 三條垂直平分線共點的證明 | proof of concurrency of perpendicular bisectors
03:31 – 外心的特性 | properties of circumcentre