Hipparchus also might hаvе dеvеlореd аnd uѕеd thе theorem in рlаnе geometry саllеd Ptоlеmу'ѕ thеоrеm, because it was рrоvеd bу Ptоlеmу in hiѕ Almаgеѕt (I.10) (lаtеr elaborated оn bу Carnot).
