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