焦點 F 和三角頂點 A,B,C 共圓

參考下圖，試以滑鼠移動拋物線上的藍點，改變 A,B,C 的位置，觀察 F,A,B,C 的關係。

Sorry, the GeoGebra Applet could not be started. Please make sure that Java 1.4.2 (or later) is installed and active in your browser (Click here to install Java now)

JOHN NG, 製作軟體： GeoGebra