Author note — to cover

Angles on one side of a straight line sum to 180 degrees, with several unknowns, algebraic angles, and the check that the line really is straight before the rule is claimed. Reason stated every time. Co-interior angles, which also sum to 180, are their own page. Both tiers. (G3)

• Fluency — direct questions on angles on a straight line, 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).