Geometry 6.1 Polygons
Goals: Identify polygons & describe them. Determine the measure of angles in a quadrilateral. November 9, 2018 Geometry 6.1 Polygons
Polygon A plane figure made of three or more segments (sides). Each side intersects exactly two other sides at their endpoints. Polygons are named by vertices in consecutive order, going CW. November 9, 2018 Geometry 6.1 Polygons
Examples November 9, 2018 Geometry 6.1 Polygons
Sides don’t intersect at endpoints. These are NOT polygons. Figure not closed. No Sides or Segments Sides don’t intersect at endpoints. November 9, 2018 Geometry 6.1 Polygons
Naming Polygons The name tells you how many sides and how many vertices the polygon has. Learn the names: memorize! Be able to spell them. November 9, 2018 Geometry 6.1 Polygons
Triangle – 3 sides C Name: ABC A B November 9, 2018 Geometry 6.1 Polygons
Quadrilateral – 4 sides Q T R S Name: QRST November 9, 2018 Geometry 6.1 Polygons
Pentagon – 5 sides N Name: JKLMN M J K L November 9, 2018 Geometry 6.1 Polygons
Hexagon – 6 sides C B A D E F Name: FEDCBA November 9, 2018 Geometry 6.1 Polygons
Heptagon – 7 sides November 9, 2018 Geometry 6.1 Polygons
Octagon – 8 sides November 9, 2018 Geometry 6.1 Polygons
Nonagon – 9 sides November 9, 2018 Geometry 6.1 Polygons
Decagon – 10 sides November 9, 2018 Geometry 6.1 Polygons
More than 10 sides: n-gon 14-gon has 14 sides. 200-gon has 200 sides. November 9, 2018 Geometry 6.1 Polygons
Diagonals A segment that joins two non-consecutive vertices. November 9, 2018 Geometry 6.1 Polygons
Convex & Concave All polygons are either convex or concave. It’s easy to determine which category falls in just by looking. November 9, 2018 Geometry 6.1 Polygons
Convex All diagonals are in the interior of the polygon. November 9, 2018 Geometry 6.1 Polygons
Concave Think: Caved In At least one diagonal (or part of one) is in the exterior of the polygon. November 9, 2018 Geometry 6.1 Polygons
Equilateral Polygons All sides are congruent. November 9, 2018 Geometry 6.1 Polygons
Equiangular Polygons All the angles have the same measure. November 9, 2018 Geometry 6.1 Polygons
REGULAR Polygons Are equilateral AND equiangular. November 9, 2018 Geometry 6.1 Polygons
Theorem 6.1 The sum of the angles of a quadrilateral is 360. 4 1 2 3 1 + 2 + 3 + 4 = 360 November 9, 2018 Geometry 6.1 Polygons
Proof B + 1 + 3 = 180 D + 2 + 4 = 180 A B C D 3 4 1 2 B + 1 + 3 = 180 D + 2 + 4 = 180 B + D + (1 + 2) + (3 + 4) = 360 But 1 + 2 = A and 3 + 4 = C B + D + A + C = 360 November 9, 2018 Geometry 6.1 Polygons
Example Solve for x. x 55 55 x + x + 55 + 55 = 360 2x + 110 = 360 November 9, 2018 Geometry 6.1 Polygons
Your Turn Find the measure of each angle. A D B C (5x + 10) November 9, 2018 Geometry 6.1 Polygons
Solution 80 132 82 66 A D B C (5x + 10) (4x + 10) (3x + 40) (5x + 10) + (8x + 20) + (3x + 40) + (4x + 10) = 360 20x + 80 = 360 20x = 280 x = 14 November 9, 2018 Geometry 6.1 Polygons