Author note — to cover (Higher)

Higher only (G10): the angle subtended by a diameter is 90 degrees; spot the diameter that triggers the theorem, combine with triangle angle sums, and quote the reason precisely. Often paired with tangent facts. The proof, via the angle at the centre, belongs to Proving the circle theorems. (G10)

• Fluency — direct questions on the angle in a semicircle, 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).