<Tr> <Th> Area </Th> <Td> various methods; see below </Td> </Tr> <Tr> <Th> Internal angle (degrees) </Th> <Td> 60 ° (for equilateral) </Td> </Tr> <P> A triangle is a polygon with three edges and three vertices . It is one of the basic shapes in geometry . A triangle with vertices A, B, and C is denoted △ A B C (\ displaystyle \ triangle ABC). </P> <P> In Euclidean geometry any three points, when non-collinear, determine a unique triangle and simultaneously, a unique plane (i.e. a two - dimensional Euclidean space). In other words, there is only one plane that contains that triangle, and every triangle is contained in some plane . If the entire geometry is only the Euclidean plane, there is only one plane and all triangles are contained in it; however, in higher dimensional Euclidean spaces this is no longer true . This article is about triangles in Euclidean geometry, and, in particular, the Euclidean plane, except where otherwise noted . </P>

What is the definition of triangle in math