A triangle is a polygon with three sides and three vertices. It is one of the most basic shapes in geometry. Every triangle has three corners called vertices, three sides connecting these vertices, and three angles formed where the sides meet.
Triangles can be classified in different ways. By their sides, we have three types. An equilateral triangle has all three sides equal in length. An isosceles triangle has exactly two sides equal. A scalene triangle has all three sides of different lengths.