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
Equilateral pentagon are sufficient to determine a convex equilateral pentagon. Each circle's center is one of four vertices of the pentagon. The remaining vertex is determined by one of the intersection points of the first and the last circle of the chain. It is possible to describe any convex equilateral pentagon with only two angles α and β with α ≥ β provided the fourth angle (δ) is the smallest of the rest of the angles. Thus the general equilateral pentagon can be regarded as a bivariate function "f(α, β)" where the rest of the angles can be obtained by using trigonometric