Paper 2 · Trigonometry Lesson 7 of 13

Trigonometry 4.6 – Trig proof 2

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You’ll learn

  • Prove the sine rule for an acute triangle by dropping a perpendicular height
  • Express h two ways with SOHCAHTOA and equate to get a/sin A = b/sin B
  • Prove the obtuse case using the supplementary identity sin(180° − B) = sin B
  • Close the proof by symmetry to include the third fraction c/sin C

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