Grade 11 · Mathematics
Sine law
Why it matters
Solving oblique triangles.
Core20m readingPrerequisite: Angles & ratios
What is the sine law?
Short answer
The sine law (law of sines) relates the sides of any triangle to the sines of their opposite angles: a/sin A = b/sin B = c/sin C. It lets you solve non-right triangles when you know two angles and a side, or two sides and an angle opposite one of them. It complements the cosine law for oblique triangles.
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Frequently asked questions
- When do you use the sine law?
- When you know two angles and any side, or two sides and an angle opposite one of them, in a non-right triangle.
- What is the ambiguous case?
- When two sides and a non-included angle are given, the sine law can yield zero, one, or two possible triangles.