Polygon
A closed two-dimensional shape that is made up entirely of line segments, where each line segment connects to exactly two other line segments, one at each endpoint.
Vertex
The point where two segments meet.
Concave polygons
Polygons in which the inside angle of at least one vertex is greater than 180�.
Convex polygons
Polygons in which the inside angle of every vertex is less than or equal to 180�.
Diagonal
A line segment that extends from one vertex of the polygon to a nonadjacent vertex.
Exterior Angle
The angle between an edge of the polygon and the extension of an adjacent line segment outward from the polygon in the direction of the first edge.
Scale Factor
A ratio of the lengths of the corresponding sides of two similar polygons.
Regular Polygon
A convex polygon that is both equilateral and equiangular.
Inscribed
A polygon inside a circle, with each vertex of the polygon falling on the circumference of the circle.
Center
A coplanar point that is equidistant from every vertex of a polygon.
Radius
The distance from the center to any vertex.
Central angles
Angles formed by rays extending from the center of the regular polygon through adjacent vertices.
Apothem
The distance from the center of a regular polygon to the midpoint of a side.
Parallelogram
A special type of quadrilateral, that has two pairs of parallel lines that intersect each other.
Trapezoid
A convex quadrilateral with exactly one pair of parallel sides.
Bases
The set of parallel sides of a trapezoid.
Legs
The two sides that connect the bases of a trapezoid.
Base angles
The angles formed from a vertex joining a leg and a base of a trapezoid.
Rhombus
A quadrilateral with sides that are all congruent and opposite angles are congruent.
Square
A parallelogram that has four congruent sides and four right angles.
Area Addition Postulate
The principle of combining areas.
Composite Figure
A figure composed of two or more shapes.
Rotational symmetry
This divides an object into more than two congruent parts.
Line symmetry
This divides an object into two congruent parts.
Equilateral
A polygon, in which, all sides are equal in length.
Equiangular
A polygon, in which, all of the interior angles at the vertices are equal.