Brainlag PlusThe sine rule, the cosine rule and area = ½ab sin C for triangles without a right angle, and how to choose between them.
Letters that face each other
Label the angles A, B, C and the sides opposite them a, b, c.
Side a faces angle A.
sine rule: a/sin A = b/sin B = c/sin C
cosine rule: a² = b² + c² − 2bc cos A
area = ½ab sin C
The rest of this lesson and its 8 practice questions are in Plus.
Screen 1 of 4, free to read.
- 8 exam-style questions, marked as you go, each with a worked solution
- Anything you get wrong is saved to your flashcards