Convex polygon

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An example of a convex polygon: a regular pentagon. Pentagon.svg
An example of a convex polygon: a regular pentagon.

In geometry, a convex polygon is a polygon that is the boundary of a convex set. This means that the line segment between two points of the polygon is contained in the union of the interior and the boundary of the polygon. In particular, it is a simple polygon (not self-intersecting). [1] Equivalently, a polygon is convex if every line that does not contain any edge intersects the polygon in at most two points.

Contents

A strictly convex polygon is a convex polygon such that no line contains two of its edges. In a convex polygon, all interior angles are less than or equal to 180 degrees, while in a strictly convex polygon all interior angles are strictly less than 180 degrees.

Properties

The following properties of a simple polygon are all equivalent to convexity:

Additional properties of convex polygons include:

Every polygon inscribed in a circle (such that all vertices of the polygon touch the circle), if not self-intersecting, is convex. However, not every convex polygon can be inscribed in a circle.

Strict convexity

The following properties of a simple polygon are all equivalent to strict convexity:

Every non-degenerate triangle is strictly convex.

See also

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In geometry, a polygon is a plane figure made up of line segments connected to form a closed polygonal chain.

<span class="mw-page-title-main">Quadrilateral</span> Polygon with four sides and four corners

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<span class="mw-page-title-main">Triangle</span> Shape with three sides

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<span class="mw-page-title-main">Rectangle</span> Quadrilateral with four right angles

In Euclidean plane geometry, a rectangle is a quadrilateral with four right angles. It can also be defined as: an equiangular quadrilateral, since equiangular means that all of its angles are equal ; or a parallelogram containing a right angle. A rectangle with four sides of equal length is a square. The term "oblong" is occasionally used to refer to a non-square rectangle. A rectangle with vertices ABCD would be denoted as  ABCD.

<span class="mw-page-title-main">Kite (geometry)</span> Quadrilateral symmetric across a diagonal

In Euclidean geometry, a kite is a quadrilateral with reflection symmetry across a diagonal. Because of this symmetry, a kite has two equal angles and two pairs of adjacent equal-length sides. Kites are also known as deltoids, but the word deltoid may also refer to a deltoid curve, an unrelated geometric object sometimes studied in connection with quadrilaterals. A kite may also be called a dart, particularly if it is not convex.

<span class="mw-page-title-main">Parallelogram</span> Quadrilateral with two pairs of parallel sides

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<span class="mw-page-title-main">Rhombus</span> Quadrilateral with sides of equal length

In plane Euclidean geometry, a rhombus is a quadrilateral whose four sides all have the same length. Another name is equilateral quadrilateral, since equilateral means that all of its sides are equal in length. The rhombus is often called a "diamond", after the diamonds suit in playing cards which resembles the projection of an octahedral diamond, or a lozenge, though the former sometimes refers specifically to a rhombus with a 60° angle, and the latter sometimes refers specifically to a rhombus with a 45° angle.

<span class="mw-page-title-main">24-cell</span> Regular object in four dimensional geometry

In four-dimensional geometry, the 24-cell is the convex regular 4-polytope (four-dimensional analogue of a Platonic solid) with Schläfli symbol {3,4,3}. It is also called C24, or the icositetrachoron, octaplex (short for "octahedral complex"), icosatetrahedroid, octacube, hyper-diamond or polyoctahedron, being constructed of octahedral cells.

<span class="mw-page-title-main">Decagon</span> Shape with ten sides

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In Euclidean geometry, a regular polygon is a polygon that is direct equiangular and equilateral. Regular polygons may be either convex, star or skew. In the limit, a sequence of regular polygons with an increasing number of sides approximates a circle, if the perimeter or area is fixed, or a regular apeirogon, if the edge length is fixed.

<span class="mw-page-title-main">Concyclic points</span> Points on a common circle

In geometry, a set of points are said to be concyclic if they lie on a common circle. A polygon whose vertices are concyclic is called a cyclic polygon, and the circle is called its circumscribing circle or circumcircle. All concyclic points are equidistant from the center of the circle.

<span class="mw-page-title-main">Semicircle</span> Geometric shape

In mathematics, a semicircle is a one-dimensional locus of points that forms half of a circle. It is a circular arc that measures 180°. It has only one line of symmetry.

<span class="mw-page-title-main">Square</span> Regular quadrilateral

In Euclidean geometry, a square is a regular quadrilateral, which means that it has four equal sides and four equal angles. It can also be defined as a rectangle with two equal-length adjacent sides. It is the only regular polygon whose internal angle, central angle, and external angle are all equal (90°), and whose diagonals are all equal in length. A square with vertices ABCD would be denoted ABCD.

<span class="mw-page-title-main">120-cell</span> Four-dimensional analog of the dodecahedron

In geometry, the 120-cell is the convex regular 4-polytope (four-dimensional analogue of a Platonic solid) with Schläfli symbol {5,3,3}. It is also called a C120, dodecaplex (short for "dodecahedral complex"), hyperdodecahedron, polydodecahedron, hecatonicosachoron, dodecacontachoron and hecatonicosahedroid.

<span class="mw-page-title-main">Simple polygon</span> Shape bounded by non-intersecting line segments

In geometry, a simple polygon is a polygon that does not intersect itself and has no holes. That is, it is a piecewise-linear Jordan curve consisting of finitely many line segments. These polygons include as special cases the convex polygons, star-shaped polygons, and monotone polygons.

<span class="mw-page-title-main">Dual polygon</span>

In geometry, polygons are associated into pairs called duals, where the vertices of one correspond to the edges of the other.

<span class="mw-page-title-main">Pentagon</span> Shape with five sides

In geometry, a pentagon is any five-sided polygon or 5-gon. The sum of the internal angles in a simple pentagon is 540°.

<span class="mw-page-title-main">Convex curve</span> Type of plane curve

In geometry, a convex curve is a plane curve that has a supporting line through each of its points. There are many other equivalent definitions of these curves, going back to Archimedes. Examples of convex curves include the convex polygons, the boundaries of convex sets, and the graphs of convex functions. Important subclasses of convex curves include the closed convex curves, the smooth curves that are convex, and the strictly convex curves, which have the additional property that each supporting line passes through a unique point of the curve.

In geometry, a circular triangle is a triangle with circular arc edges.

References

  1. Definition and properties of convex polygons with interactive animation.
  2. Chandran, Sharat; Mount, David M. (1992). "A parallel algorithm for enclosed and enclosing triangles". International Journal of Computational Geometry & Applications. 2 (2): 191–214. doi:10.1142/S0218195992000123. MR   1168956.
  3. Weisstein, Eric W. "Triangle Circumscribing". Wolfram Math World.
  4. Lassak, M. (1993). "Approximation of convex bodies by rectangles". Geometriae Dedicata. 47: 111–117. doi:10.1007/BF01263495. S2CID   119508642.
  5. Belk, Jim. "What's the average width of a convex polygon?". Math Stack Exchange.