Equilateral polygon with 60° internal angles. An equilateral quadrilateral is called a rhombus, an isotoxal polygon described by an angle α. It includes the square as a special case. A convex equilateral pentagon can be described by two angles α and β, which together determine the other angles. Concave equilateral pentagons exist, as do concave equilateral polygons with any larger number of sides. An equilateral polygon which is cyclic (its vertices are on a circle) is a regular polygon (a polygon that is both equilateral and equiangular). A tangential polygon (one that has an incircle tangent to all its sides) is equilateral
Triangle (musical instrument) form of an equilateral triangle, early instruments were often formed as non-equilateral isosceles triangles. In the early days the triangles did not have an opening and had jingling rings along the lower side. Early examples of triangles include ornamental work at the open end, often in a scroll pattern. Historically, the triangle has been manufactured from a solid iron and later steel rod and bent into a triangular shape roughly equilateral. In modern times, the scroll pattern has been abandoned and triangles are made from either steel or brass. The triangle is often the subject of jokes and one liners