Triangle - perimeter

A triangle is a polygon with three edges and three vertices, and it is one of the basic shapes in geometry. The sum of the internal angles of a triangle is always 180 degrees. Triangles can be classified based on their side lengths or their internal angles: by side lengths, there are equilateral triangles with all three sides of equal length and all three internal angles of 60 degrees, isosceles triangles with two sides of equal length and two equal internal angles, and scalene triangles with all three sides and internal angles different; by internal angles, there are acute triangles with all three internal angles less than 90 degrees, right triangles with one internal angle of exactly 90 degrees, and obtuse triangles with one internal angle greater than 90 degrees. Triangles are fundamental in many areas of mathematics and are used in various applications in science, engineering, and art.