Author note — to cover

Find and use nth terms of decreasing linear sequences, where a negative common difference gives forms like 23 − 3n; generate terms, find where the sequence turns negative, and test membership. Both tiers under A25's linear sequences; the sign of the constant is the mark to protect. (A25)

• Fluency — direct questions on decreasing linear sequences, 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).