https://www.geogebra.org/m/JKAusfRR

[size=85]https://www. ggbm.at/KnfUCy7G[/size]

[size=85]https://www.nctm.org/Classroom-Resources/Illuminations/Interactives/Circle-Tool/[br](Flash Player required)[/size]

[size=85]https://www.ggbm.at/Z5dsTpDm[/size]

[size=85]https://www.pbs.org/wgbh/nova/assets/swf/1/approximating-pi/approximating-pi.swf[br](Flash Player required)[/size]

http://www.hkedcity.net/edb/teachingresources/files/pmaths/circle/cir_webMAIN.html[br](Flash Player required)