These 2 rules are used with **non-right angle triangles**. Which one to use will depend on the data you are given.

**The Convention**

**Note**: The convention on labelling the triangle is:
- Angles are in CAPITALS
- Sides are in lower case

In addition, each angle/side pair is such that
- Angle **A** MUST BE opposite side **a**
- Angle **B** MUST BE opposite side **b**
- Angle **C** MUST BE opposite side **c**

**The Sine Rule**

Use this rule when you are given **AN ANGLE AND ITS OPPOSITE SIDE**.

Below are 2 examples using both versions of the sine rule.

**The Cosine Rule**

The rule can be written in the following two versions

2 scenarios when the Cosine rule is used

- When you have 2 sides and the angle
**between** the 2 sides - When you have all 3 sides of the triangle.

Watch this short video for examples of using the Cosine rule.

The full video lesson on the Sine & Cosine rules can be found **here**.

These 2 rules are used with

non-right angle triangles. Which one to use will depend on the data you are given.The ConventionThe Sine RuleUse this rule when you are given

AN ANGLE AND ITS OPPOSITE SIDE.Below are 2 examples using both versions of the sine rule.

The Cosine RuleThe rule can be written in the following two versions

2 scenarios when the Cosine rule is used

betweenthe 2 sidesWatch this short video for examples of using the Cosine rule.

## Nouri Dib