1. 13-5 Law of Cosines Objective:
To solve triangles by using the law of cosines.

2. Law of Cosines
Let ∆ABC be any triangle with a, b, and c representing the measures of sides opposite angles with measures A, B, and C respectively. Then the following equations hold true.

3. In order to use the Law of Cosines…
You need the measure of two sides and the included angle.
You need the measures of all three sides.

4. Example 1
For ∆ABC, find a if measure of angle A = 52°, c = 7, and b = 4.

5. Example 2
Solve ∆UVW if the measure of angle U = 41°, v = 13, and w = 12.

6. What if you have no angles?

7. Assignment
13-5 Worksheet