This study notes covers Worked Example 1: Interior Angle Sum within Angles in Polygons for GCSE Mathematics. Revise Angles in Polygons in Geometry & Measures for GCSE Mathematics with 12 exam-style questions and 3 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 4 of 10 in this topic. Use this study notes to connect the idea to the wider topic before moving on to questions and flashcards.
Worked Example 1: Interior Angle Sum
Find the sum of interior angles in a nonagon (9-sided polygon).
Step 1 Use the formula
Sum = (n − 2) × 180°
n = 9
Step 2 Calculate
Sum = (9 − 2) × 180°
Sum = 7 × 180° = 1260°
Practice questions for Angles in Polygons
What is the sum of the interior angles of a hexagon?
Explain how the formula (n − 2) × 180° for the sum of interior angles of a polygon is derived.
Quick recall flashcards
Exterior Angle Sum
Always 360° for any polygon
Interior Angle Sum
Sum = (n - 2) × 180° for n-sided polygon