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Polygons Vocabulary


acute triangle A triangle with all angles measures less than 90 degrees.
isosceles triangle A triangle with at least two congruent sides; two side lengths are the same.
right triangle A triangle with one 90 degree angle.
scalene triangle A triangle that has NO congruent sides; all side lengths are different.
equilateral triangle A triangle with three congruent sides; all side lengths have the same measure.
obtuse A triangle with one obtuse angle; one angle measure is greater than 90 degrees.
triangle A three sided polygon.
triangle sum theorem The theorem which states that the angles measures of any triangle must have a sum of 180 degrees; the angles of a triangle add up to 180 degrees.
leg In a right triangle, the legs are the two sides which create the right angle; the perpendicular line segments.
hypotenuse In a right triangle, the side opposite the right angle; the longest side in a right triangle. The side of the triangle that is does not create the right angle.
triangle inequality The rule that says the smallest side length plus the medium side length must have a sum greater than the largest side length. Small + Medium > Large
3 sided shape triangle
4 sided shape quadrilateral
5 sided shape pentagon
6 sided shape hexagon
7 sided shape septagon or heptagon
8 sided shape octagon
9 sided shape nonagon
10 sided shape decagon
11 sided shape hendecagon or an 11-gon
12 sided shape dodecagon
15 sided shape pentadecagon
Sum of the interior angles of a polygon (n-2) x 180 where n is the number of sides on the polygon
Number of triangles formed when a polygon is divided into triangles using diagonals (triangulation) n-2 (n is the number of sides)
The measure of each interior angle of a regular polygon Sum of the interior angles / number of sides
Triangulate or Triangulation The process of dividing a polygon into triangles by drawing its diagonals
Polygon A closed plane figure created by three or more line segments that intersect only at their endpoints (vertices)
Regular Polygon A polygon with congruent sides and angles
Congruent Having the same size and shape
Created by: theboss1000
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