Triangle
2D shape
A triangle is a polygon with three corners and three sides, one of the basic shapes in geometry. The corners, also called vertices, are zero-dimensional points while the sides connecting them, also called edges, are one-dimensional line segments.... Wikipedia
Area: various methods; see below
Longest side: the hypotenuse
Sum of interior angles: 180°
Number of edges: 3
Number of vertices: 3
Line of symmetry: 3
Rotational symmetry order: 3