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It is always possible to partition a concave polygon into a set of convex polygons. A polynomial-time algorithm for finding a decomposition into as few convex polygons as possible is described by Chazelle & Dobkin (1985). [5] A triangle can never be concave, but there exist concave polygons with n sides for any n > 3.
Except in the triangle case, an equilateral polygon does not need to also be equiangular (have all angles equal), but if it does then it is a regular polygon. If the number of sides is at least four, an equilateral polygon does not need to be a convex polygon: it could be concave or even self-intersecting.
A rectilinear polygon has corners of two types: corners in which the smaller angle (90°) is interior to the polygon are called convex and corners in which the larger angle (270°) is interior are called concave. [1] A knob is an edge whose two endpoints are convex corners. An antiknob is an edge whose two endpoints are concave corners. [1]
Fan triangulation of a convex polygon Fan triangulation of a concave polygon with a unique concave vertex.. In computational geometry, a fan triangulation is a simple way to triangulate a polygon by choosing a vertex and drawing edges to all of the other vertices of the polygon.
The 42 possible triangulations for a convex heptagon (7-sided convex polygon). This number is given by the 5th Catalan number. It is trivial to triangulate any convex polygon in linear time into a fan triangulation, by adding diagonals from one vertex to all other non-nearest neighbor vertices.
Convex equilateral pentagon dissected into 3 triangles, which helps to calculate the value of angle δ as a function of α and β. When a convex equilateral pentagon is dissected into triangles, two of them appear as isosceles (triangles in orange and blue) while the other one is more general (triangle in green).
If p = 2, draw a q-gon and bisect one of its central angles. From this, a 2q-gon can be constructed. If p > 2, inscribe a p-gon and a q-gon in the same circle in such a way that they share a vertex. Because p and q are coprime, there exists integers a and b such that ap + bq = 1. Then 2aπ/q + 2bπ/p = 2π/pq.
Alternatively, a Reuleaux triangle may be constructed from an equilateral triangle T by drawing three arcs of circles, each centered at one vertex of T and connecting the other two vertices. [9] Or, equivalently, it may be constructed as the intersection of three disks centered at the vertices of T, with radius equal to the side length of T. [10]