Study Notes
The Sine Rule and Cosine Rule are used to solve problems involving any triangle, not just right-angled ones.
- Sine Rule — relates the sides and angles of a triangle using the sine function. Example: Used when given two sides and an angle opposite one of these sides, or one side and any two angles.
- Cosine Rule — relates the lengths of the sides of a triangle to the cosine of one of its angles. Example: Used when given two sides and the included angle (SAS) or all three sides (SSS).
Exam Tips
Key Definitions to Remember
- Sine Rule:
- Cosine Rule:
Common Confusions
- Mixing up when to use the Sine Rule versus the Cosine Rule.
- Forgetting to use the included angle in the Cosine Rule.
Typical Exam Questions
- How do you find an unknown angle using the Sine Rule? Use the formula and solve for the angle.
- How do you find an unknown side using the Cosine Rule? Use the formula and solve for the side.
- What is the length of a side in a triangle given two sides and an included angle? Use the Cosine Rule to find the length.
What Examiners Usually Test
- Correct application of the Sine and Cosine Rules.
- Ability to identify which rule to use based on given information.
- Accuracy in calculations and rounding to the correct decimal place.