A triangle is a fundamental shape in geometry. It is a polygon with exactly three edges and three vertices. Every triangle has three sides, three vertices, and three angles. One of the most important properties of triangles is that the sum of all interior angles is always one hundred eighty degrees.
Triangles can be classified based on their side lengths. An equilateral triangle has all three sides of equal length, and all three angles are sixty degrees. An isosceles triangle has at least two sides of equal length, and the angles opposite the equal sides are also equal. A scalene triangle has all three sides of different lengths, and all three angles are different.