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Geometry
Polygons Properties
21
Mathematics
9th Grade
01/21/2009

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Term
polygon
Definition
A polygon is a closed figure made by joining line segments, where each line segment intersects exactly two others.
Term
regular polygon
Definition
A regular polygon is a polygon whose sides are all the same length, and whose angles are all the same. The sum of the angles of a polygon with n sides, where n is 3 or more, is 180° × (n - 2) degrees.
Term
triangle
Definition
A three-sided polygon. The sum of the angles of a triangle is 180 degrees.
Term
acute triangle
Definition
A triangle having three acute angles.
Term
obtuse triangle
Definition
A triangle having an obtuse angle. One of the angles of the triangle measures more than 90 degrees.
Term
right triangle
Definition
A triangle having a right angle. One of the angles of the triangle measures 90 degrees. The side opposite the right angle is called the hypotenuse. The two sides that form the right angle are called the legs. A right triangle has the special property that the sum of the squares of the lengths of the legs equals the square of the length of the hypotenuse. This is known as the Pythagorean Theorem.
Term
quadralateral
Definition
A four-sided polygon. The sum of the angles of a quadrilateral is 360 degrees.
Term
rectangle
Definition
A four-sided polygon having all right angles. The sum of the angles of a rectangle is 360 degrees.
Term
square
Definition
A four-sided polygon having equal-length sides meeting at right angles. The sum of the angles of a square is 360 degrees.

Examples:
Term
parrelogram
Definition
A four-sided polygon having equal-length sides meeting at right angles. The sum of the angles of a square is 360 degrees.

Examples:
Term
rhombus
Definition
A four-sided polygon having equal-length sides meeting at right angles. The sum of the angles of a square is 360 degrees.

Examples:
Term
trapezoid
Definition
A four-sided polygon having exactly one pair of parallel sides. The two sides that are parallel are called the bases of the trapezoid. The sum of the angles of a trapezoid is 360 degrees.
Term
pentagon
Definition
A five-sided polygon. The sum of the angles of a pentagon is 540 degrees.
Term
hexagon
Definition
A six-sided polygon. The sum of the angles of a hexagon is 720 degrees.
Term
heptagon
Definition
A seven-sided polygon. The sum of the angles of a heptagon is 900 degrees.
Term
octagon
Definition
An eight-sided polygon. The sum of the angles of an octagon is 1080 degrees.
Term
nonagon
Definition
A nine-sided polygon. The sum of the angles of a nonagon is 1260 degrees.
Term
decagon
Definition
A ten-sided polygon. The sum of the angles of a decagon is 1440 degrees.
Term
circle
Definition
A circle is the collection of points in a plane that are all the same distance from a fixed point. The fixed point is called the center. A line segment joining the center to any point on the circle is called a radius.
Term
convex
Definition
A figure is convex if every line segment drawn between any two points inside the figure lies entirely inside the figure. A figure that is not convex is called a concave figure.
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