円周率
なぜ無限なのか
https://atarimae.biz/archives/2013
円周率簡単!覚えれる
https://text.tomo.school/how-to-get-pi/
https://terakoya.ameba.jp/a000001619/#:~:text=%E7%8E%87%E3%81%A8%E3%81%AF%EF%BC%9F-,%E5%85%AC%E5%BC%8F%E3%81%AF(%E5%86%86%E5%91%A8%E3%81%AE%E9%95%B7%E3%81%95)%C3%B7(%E7%9B%B4%E5%BE%84,%E3%81%93%E3%81%A8%E3%82%92%E8%A1%A8%E3%81%97%E3%81%A6%E3%81%84%E3%81%BE%E3%81%99%E3%80%82
https://w3e.kanazawa-it.ac.jp/e-scimath/contents/t16/textbook_t16_all.pdf