Curriculum
Pure Mathematics — Second Secondary
Unit 1: Real Functions and Curve Sketching
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Unit 2: Exponents and Logarithms
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Unit 3: Limits
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Text lesson
The Sine Rule
The Sine Rule
Statement of the sine rule
Statement of the sine rule
- In any triangle ABC
- let a
- b and c be the lengths of the sides opposite the angles A
- B and C respectively. Then:
a / sin A = b / sin B = c / sin C = 2R
- where R is the radius of the circle passing through the three vertices of the triangle.
- In other words, the ratio of any side to the sine of its opposite angle is the same throughout the triangle.
- The rule is normally used in one of two situations:
Key points
Two angles and a sidethe third angle is found from the sum of the angles (180°), then the other sides are found.
Two sides and a non-included angleanother angle is found from the rule, and there may be two possible triangles.
The Sine Rule · 1 / 5