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Adjacent Sides
Sides of a polygon that share a vertex.
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Base
One of the parallel sides of a trapezoid.
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Center of a Regular Polygon
The point on the interior of a polygon from which all vertices of the polygon are equidistant.
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Closed Curve
A curve whose starting point is the same as its ending point.
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Concave Polygon
A polygon with one or more interior angles greater than 180 degrees.
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Congruent Polygons
Polygons whose sides are all congruent
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Consecutive Vertices
Vertices of a polygon that include the endpoints of the same side.
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Continuous
Without any gaps or holes.
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Convex Polygon
A polygon whose interior angles are all less than 180 degrees.
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Consecutive Angles
Angles in a polygon that share a segment as one of the sides that could be extended into a ray.
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Curve
An arrangement of continuous points in space.
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Decagon
A ten-sided polygon.
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Diagonal
A line segment joining nonconsecutive vertices of a polygon.
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Dodecagon
A twelve-sided polygon.
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Equiangular Polygon
A polygon whose angles are congruent.
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Equilateral Polygon
A polygon whose sides are congruent.
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Exterior Angle
The angle formed at a vertex of a polygon that lies outside of the region enclosed by a polygon.
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Heptagon
A seven-sided polygon.
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Hexagon
A six-sided polygon.
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Interior Angle
The angle formed, at a vertex of a polygon, that lies inside the region enclosed by the polygon.
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Leg
One of the nonparallel sides of a trapezoid.
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Median
The segment in a trapezoid whose endpoints are the midpoints of the legs of the trapezoid.
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Nonagon
A nine-sided polygon.
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Opposite sides
Sides of a quadrilateral that don't share a vertex.
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Octagon
An eight-sided polygon.
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Parallelogram
A quadrilateral with two pairs of parallel sides.
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Pentagon
A five-sided polygon.
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Polygon
A simple closed curve consisting of the union of segments that intersect each other at their endpoints.
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Quadrilateral
A four-sided polygon.
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Rectangle
A quadrilateral with four congruent angles.
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Regular Polygon
An equilateral, equiangular polygon.
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Rhombus
A quadrilateral with four congruent sides.
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Side
One segment that comprises part of a polygon.
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Simple Closed Curve
A closed curve that does not intersect itself.
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Square
A quadrilateral with four congruent sides and angles.
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Trapezoid
A quadrilateral with one pair of parallel sides.
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Triangle
A three-sided polygon.
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Vertex
The common endpoint of two sides of a polygon.
Terms
Formulae
| Diagonal Sum | A polygon with n sides has n(n-3)/2 diagonals. |
| Interior Angle Sum | The interior angle sum of a polygon with n sides is 180(n-2) degrees. |
