Geometry Concepts: Interior and Exterior Angles in Polygons

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Explore the properties of interior and exterior angles in polygons like regular hexagons, quadrilaterals, triangles, and more. Understand how to calculate angles and sums accurately to solve geometric problems.


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  1. Starter B C ABCDE is a regular hexagon with centre O. Use what you know about angle notation to write down the values of the below. 120 30 60 30 D A O 60 60 E F = 90 = 60 = 60 Find ABC ADC BAC CAD = 120 = 60 = 30 = 30 ACD ODE EOD

  2. Interior angles A quadrilateral has 4 sides. It can be split into 2 triangles. The sum of the angles of a quadrilateral = 2 x 180 = 360 . p q r p + q + r + s = 360 s

  3. Interior angles A pentagon has 5 sides. It can be split into 3 triangles. The sum of the interior angles of any pentagon = 3 x 180 = 540 q p p + q + r + s + t = 540 r s t

  4. Exterior angles b a Exterior angles of a polygon add to 360 . c a + b + c + d + e = 360 e d At each vertex: interior angle + exterior angle = 180

  5. Answers Name of regular polygon Equilateral triangle Square Pentagon Hexagon Heptagon Octagon Nonagon Decagon n-sided polygon Number of Sides Size of exterior angle Sum of all interior angles Size of interior angle 3 360 3 = 120 1 x 180 = 180 180 3 = 60 4 5 6 7 8 9 10 360 4 = 90 360 5 = 72 360 6 = 60 360 7 = 51.4 360 8 = 45 360 9 = 40 360 10 = 36 2 x 180 = 360 3 x 180 = 540 4 x 180 = 720 5 x 180 = 900 6 x 180 = 1080 7 x 180 = 1260 8 x 180 = 1440 360 4 = 90 540 5 = 108 720 6 = 120 900 7 = 128.6 1080 8 = 135 1260 9 = 140 1440 10 = 144 (n 2) x 180 n n 360 n (n 2) x 180

  6. Answers 1800 1a. 1440 b. c. 1980 2a. 12 b. 20 c. 9 3. 154.3 4. 30 5. 3600 6. Wrong 7. 60 8a. 240 b. 120

  7. Exam question ABCDEF is a regular hexagon. EFGH is a square. Angle DEH = x Work out the value of x. B C A D Ext angle of hex = 360 6 = 60 E F x Ext angle of square = 360 4 = 90 H G x = 90 + 60 = 150