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 straight sides connecting these vertices, and three interior angles.
Triangles can be classified in different ways. By their sides, we have three types. An equilateral triangle has all three sides equal. An isosceles triangle has two sides equal. A scalene triangle has all three sides of different lengths.
Triangles can also be classified by their angles. An acute triangle has all angles less than ninety degrees. A right triangle has exactly one angle equal to ninety degrees. An obtuse triangle has one angle greater than ninety degrees.
Triangles have important mathematical properties. The sum of all three interior angles in any triangle always equals one hundred eighty degrees. Another key property is the triangle inequality, which states that the sum of any two sides must be greater than the third side.
To summarize what we have learned about triangles: A triangle is a fundamental polygon with three sides and three vertices. Triangles can be classified by their sides as equilateral, isosceles, or scalene, and by their angles as acute, right, or obtuse. The sum of interior angles in any triangle always equals one hundred eighty degrees.