τρίγωνος [ῐ],ον,
A. three-cornered, triangular, τὴν τ. ἐς χθόνα Νειλῶτιν,of the Delta, A. Pr. 813 ; τ. ῥυθμοί
Id. Fr. 78
; βάσεις
Pl. Ti. 55b
; of the hearts of certain fish, Arist. Frr. 314 , 330 , 333 ; of Sicily, Plb. 1.42.3 ; of Britain, Str. 4.5.1 .
2. ἀριθμοὶ τρίγωνοι, triangularnumbers, are those whose units can be disposed in a triangle, as 3 <*>, 6 <*>, etc., being represented by the formulan(n+ 1 )/ 2 , Plu. 2.1003f , cf. Nicom. Ar. 2.8 ; these numbers are also calledtriangles(τρίγωνοι), Plu. 2.744b .
3. Astrol.,in triangularortrine aspect,of planets when there are three signs of the zodiac between them, so that they are at the apices of an equilateral triangle, S.E. M. 5.39 , Plot. 2.3.4 ; τ. σχηματισμοί
Ptol. Tetr. 35
, cf. Man. 3.344 .
II. asSubst.,τρίγωνον,τό, triangle,
Ti.Locr. 98a , Pl. Ti. 50b , etc.