1. Grade 12 Essential Math Geometry and Trigonometry Unit
Cosine Law
Grade 12 Essential Math
Geometry and Trigonometry Unit

2. Cosine Law
Cosine law is another tool we have to solve non-right angle triangles:
Formula:
𝑎 2 = 𝑏 2 + 𝑐 2 −2𝑏𝑐 cos⁡(𝐴)
In this formula, a is the side we are trying to solve for, and A is the opposing angle.

3. Cosine Law When we are trying to solve for an angle, use this formula:
In this formula, A is the angle we are trying to solve for and a is the opposing side.

4. Cosine Law To use cosine law, we need pairs of sides and angles
We need the pair that contains our unknown value, and two other sides.

5. Example
Find the missing side

6. Example
Find the missing angle:

7. Example
Find x: 81
5.6
4.5 x

8. Example
Find A:
7.4
4.1
7.2 A