1. Section 6.2
The Law of Cosines

2. About the Law of Cosines
Can be used when given two sides and the angle between them or when given three sides but no angles.
No ambiguous case.
Make sure your calculator is in DEGREE mode.
Once you identify a matched pair (an angle and its opposite side), you can resume using the Law of Sines.

3. One formula, three versions

4. Examples A = 48°, b = 9, c = 12 a = 4, b = 11, c = 8
a = 6, c = 6, B = 57°
Two ships leave a harbor at the same time. One ship travels on a bearing S10°W at 13 miles per hour. The other ship travels on a bearing N75°E at 12 miles per hour. How far apart will the ships be after 2 hours?

5. Heron’s Formula

6. Examples
Use Heron’s formula to find the area of the following triangles:
a = 8 ft, b = 8 feet, c = 1 foot
a = 2 yards, b = 12 yards, c = 13 yards