Author note — to cover (Higher)

Higher only (G22, formula to know): c squared equals a squared plus b squared minus 2ab cos C for the third side from two sides and the included angle, evaluating the subtraction last and square-rooting at the end; an obtuse included angle makes the cosine negative. (G22)

• Fluency — direct questions on the cosine rule for sides, 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).