Author note — to cover

Rearranged Pythagoras: subtract squares when the hypotenuse is already known — the error-prone swap, named and drilled — with isosceles-triangle heights and ladder contexts. Purely right-angled 2D work; the cosine rule generalisation is Higher, in the sine-and-cosine-rules group. Both tiers. (G20)

• Fluency — direct questions on finding a shorter side, 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).