A triangle is a polygon with three edges and three vertices. Triangle is one of the basic shapes in geometry. A triangle with vertices A, B, and C is denoted. In Euclidean geometry, any three points, when non-collinear, determine a unique triangle and simultaneously, a unique plane. Because of a triangle's relationship between intersecting angles and length, triangles may be the most reliable shape in architecture. When you change the angle of a triangle, you change its length as well. The triangle is a stable shape that is a great weight bearer because it's widest at its base. Two triangles are congruent if two angles and the included side of one triangle are equal to the corresponding two angles and the included side of the other triangle.