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Study Guide for the Interior Angles of Polygons

Quiz yourself by thinking what should be in each of the black spaces below before clicking on it to display the answer.
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Question
Answer
Explain how to use the number of sides to find the sum of the interior angles of polygons.   (n-2) x 180 = the sum of the interior angles of a polygon  
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Explain how to use the number of sides to find one angle measure of a regular polygon.   (n-2) x 180 = the sum of the interior angles of a polygon. Divide this number by the number of sides.  
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What are the differences between a regular and an irregular polygon?   Regular polygons have side and interior angle measurements that are are congruent.Irregular polygons do not have congruent side or interior angle measurements.  
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Why is it important to know if a polygon is regular or irregular when determining angle measurements?   With regular polygons you can use the rule (n-2)x180/n. With irregular polygons you cannot use this rule because the angles are not congruent.  
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Find the sum of the interior angles of a nonagon.   1260 degrees  
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Find the sum of the interior angles of a hexagon.   720 degrees  
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Find the sum of the interior angles of a decagon.   1440 degrees  
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Find the sum of the interior angles of a 18-gon.   2880 degrees  
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Find the measure of one interior angle for a regular pentagon.   108 degrees  
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Find the measure of one interior angle for a regular 12 sided figure.   150 degrees  
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Find the measure of one interior angle for a regular octagon   135 degrees  
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Explain how to use the number of sides to determine the number of triangles needed to triangulate the figure.   The number of sides minus 2 is equal to the number of triangles.  
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Explain how triangulating a polygon can be used to find the sum of the interior angles of a polygon.   The number of triangles multiplied by the 180 is equal to the sum of the interior angles.  
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What is the easiest way to triangulate a polygon?   Start from one vertex to draw non-intersecting diagonals.  
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What is the measure of one angle of a regular hexagon?   120 degrees  
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What is the measure of one angle of a regular nonagon?   140 degrees  
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A regular pentagon and an irregular pentagon both have the same total interior angle measurement. True or False   True. It does not matter if a polygon is regular or irregular. The interior angle measure is always the same.  
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Angles of a regular polygon are not equal. True or False   False. Regular polygons have angles with congruent measurements.  
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Regular polygons have both congruent sides and congruent angles. True or False   True. Regular polygons have congruent angles and sides.  
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A rectangle is a regular polygon. True or False   False. A rectangle has congruent angles, but it does not have congruent sides.  
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A square is a regular polygon. True or False   True. A square has congruent angles and sides so it is a regular polygon.  
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acute triangle   A triangle with all angles measures less than 90 degrees.  
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isosceles triangle   A triangle with at least two congruent sides; two side lengths are the same.  
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right triangle   A triangle with one 90 degree angle.  
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scalene triangle   A triangle that has NO congruent sides; all side lengths are different.  
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equilateral triangle   A triangle with three congruent sides; all side lengths have the same measure.  
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obtuse   A triangle with one obtuse angle; one angle measure is greater than 90 degrees.  
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triangle   A three sided polygon.  
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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.  
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leg   In a right triangle, the legs are the two sides which create the right angle; the perpendicular line segments.  
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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.  
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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  
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3 sided shape   triangle  
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4 sided shape   quadrilateral  
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5 sided shape   pentagon  
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6 sided shape   hexagon  
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7 sided shape   septagon or heptagon  
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8 sided shape   octagon  
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9 sided shape   nonagon  
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10 sided shape   decagon  
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11 sided shape   hendecagon or an 11-gon  
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12 sided shape   dodecagon  
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15 sided shape   pentadecagon  
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Sum of the interior angles of a polygon   (n-2) x 180 where n is the number of sides on the polygon  
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Number of triangles formed when a polygon is divided into triangles using diagonals (triangulation)   n-2 (n is the number of sides)  
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The measure of each interior angle of a regular polygon   Sum of the interior angles / number of sides  
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Triangulate or Triangulation   The process of dividing a polygon into triangles by drawing its diagonals  
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Polygon   A closed plane figure created by three or more line segments that intersect only at their endpoints (vertices)  
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Regular Polygon   A polygon with congruent sides and angles  
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Congruent   Having the same size and shape  
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Explain how to use the number of sides to find the sum of the interior angles of polygons.   (n-2) x 180 = the sum of the interior angles of a polygon  
🗑
Explain how to use the number of sides to find one angle measure of a regular polygon.   (n-2) x 180 = the sum of the interior angles of a polygon. Divide this number by the number of sides.  
🗑
What are the differences between a regular and an irregular polygon?   Regular polygons have side and interior angle measurements that are are congruent.Irregular polygons do not have congruent side or interior angle measurements.  
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Why is it important to know if a polygon is regular or irregular when determining angle measurements?   With regular polygons you can use the rule (n-2)x180/n. With irregular polygons you cannot use this rule because the angles are not congruent.  
🗑
Find the sum of the interior angles of a nonagon.   1260 degrees  
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Find the sum of the interior angles of a hexagon.   720 degrees  
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Find the sum of the interior angles of a decagon.   1440 degrees  
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Find the sum of the interior angles of a 18-gon.   2880 degrees  
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Find the measure of one interior angle for a regular pentagon.   108 degrees  
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Find the measure of one interior angle for a regular 12 sided figure.   150 degrees  
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Find the measure of one interior angle for a regular octagon.   135 degrees  
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Explain how to use the number of sides to determine the number of triangles needed to triangulate the figure.   The number of sides minus 2 is equal to the number of triangles.  
🗑
Explain how triangulating a polygon can be used to find the sum of the interior angles of a polygon.   The number of triangles multiplied by the 180 is equal to the sum of the interior angles.  
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What is the easiest way to triangulate a polygon?   Start from one vertex to draw non-intersecting diagonals.  
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