Reference:[br][list=1][*][url=https://www.geogebra.org/m/mAGesaxF]https://www.geogebra.org/m/mAGesaxF[/url] by Michael Borcherds [br][/*][*][url=https://www.geogebra.org/m/fzqM2u6s]https://www.geogebra.org/m/fzqM2u6s[/url] by Anthony Or[/*][*]Image source: [url=https://missminded.deviantart.com/art/Clock-Face-147533631]https://missminded.deviantart.com/art/Clock-Face-147533631[/url][/*][/list][br]gMath 互動數學教室 [url=http://www.geogebra.hk/]http://www.geogebra.hk[/url]