Author note — to cover

The exterior angle equals the sum of the two opposite interior angles: derive it from the angle sum and the straight line, use it as a one-step shortcut, and quote it as a named reason. Polygon exterior angles are a separate page. Both tiers. (G3, G6)

• Fluency — direct questions on the exterior angle of a triangle, 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).