Author note — to cover

Angle sum (n minus 2) times 180 derived by splitting into triangles, the quadrilateral's 360 included; find missing angles in irregular polygons and recover the number of sides from a given angle sum. Regular-polygon formulas and exterior angles each have their own sibling page. Both tiers. (G3)

• Fluency — direct questions on interior angles of a polygon, limited to this lesson's stated scope (4 questions).
• Application — use the same skill in unfamiliar or contextual questions without introducing a later method (4 questions).
• Check — questions built around the exclusions and likely misconceptions named in the lesson brief (4 questions).