Author note — to cover

Half base times height with the perpendicular height, never the slant side, in any orientation including obtuse triangles where the height falls outside. G16 lists this formula among those to know and apply. The Higher alternative half ab sin C has its own page in the sine-and-cosine-rules group. Both tiers. (G16)

• Fluency — direct questions on area of a triangle, 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).