Planes, Mirrors & Exact Trigonometry | IB Math AA HL May 2025 Paper 1 Q11

How do two planes become a pair of mirrors in one perpendicular section? Build plane normals, separate the obtuse normal angle from the acute plane angle, construct the section through R and use reflection geometry with exact trigonometry and the sine rule. This is the complete 17-mark question. Source question: May 2025 IB Mathematics AA HL, Paper 1, Question 11 (17 marks). Paper code: 2225-7106. Pause at the question, try it yourself, then follow the complete explanation. English subtitles are available. CHAPTERS 00:00 A complete question: planes become mirrors 00:43 (a): use the planes to build their normals 01:23 (a): the obtuse normals and acute planes 02:05 (b): perpendicular to both original normals 02:48 (b): translate the section plane through R 03:35 Read the reflection in the perpendicular section 04:17 The ray fixes all three angles 04:59 (c)(i): turn75 degrees into familiar angles 05:44 (c)(i): keep both exact products 06:26 (c)(ii): match sides with opposite angles 07:12 (c)(ii): substitute the proved sine value 07:53 (c)(ii): rationalize into the requested form 08:35 One geometry, four assessed leaves Explore IBvia learning resources and expert support: https://ibvia.com/ IBvia is an independent educational provider and is not affiliated with or endorsed by the International Baccalaureate Organization. #IBMath #Mathematics #IBvia