John Casey | |
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| Born | 12 May 1820 |
| Died | 3 January 1891 (aged 70) |
| Education | Trinity College Dublin |
| Occupation(s) | geometer, teacher |
| Employer(s) | University College, Stephen's Green |
| Known for | Casey's theorem |
| Father | William Casey |
John Casey (12 May 1820, Kilbehenny, County Limerick, Ireland – 3 January 1891, Dublin) was a respected Irish geometer. He is most famous for Casey's theorem on a circle that is tangent to four other circles, an extension of Ptolemy's theorem. However, he contributed several novel proofs and perspectives on Euclidean geometry. He and Émile Lemoine are considered to be the co-founders of the modern geometry of the circle and the triangle.[1]
- ^ In tribute to John Casey, founder of modern geometry The Irish Times, May 12, 2020