✗ Wrong: Using (n) × 180° instead of (n − 2) × 180°
✓ Right: Always subtract 2 from the number of sides first
✗ Wrong: Interior angle = 360° ÷ n
✓ Right: That's the EXTERIOR angle! Interior = 180° − (360° ÷ n)
✗ Wrong: Sum of exterior angles = (n − 2) × 180°
✓ Right: Exterior angles ALWAYS sum to 360° (any polygon!)
This study notes covers Common Mistakes 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 8 of 10 in this topic. Use this study notes to connect the idea to the wider topic before moving on to questions and flashcards.
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