EntityQ377047· pop 25· linked from 7 articlesbutterfly theoremSign in to savetheoremConnectionscircleEntityWilliam HerschelEntityEuclidean geometryEntitychordEntityperpendicularityEntityprojective geometryEntityMathWorldEntitymidpointEntityEric W. WeissteinEntityPlanetMathEntityWilliam WallaceEntityintersecting chords theoremEntityWolfram Demonstrations ProjectEntityZassenhaus lemmaEntityForum GeometricorumEntityAlexander BogomolnyEntityCategoriesEuclidean plane geometryTheorems about circles