1. Section 6.5 Law of Cosines Objectives:
Use the Law of Cosines to solve triangles.
Use Heron’s Formula to find the area of a triangle.

2. Law of Cosines:

3. If you need to solve for an angle you will want to use these formulas instead.

4. Ex 1. Solve the triangle. B A C 5 8 12

5. Ex 2. Solve the triangle. C 76 39 A B 63

6. Ex 3. Solve ABC given A=25, b = 10, c = 20

7. EX 4. Solve for x.

8. 7. Determine whether you need to use the Law of Sines or the Law of Cosines to solve. Then find either x or . a) b) c) d)

9. Heron’s Formula:

10. Ex 5. Find the area of the triangle with sides a =15, b = 23, c = 16.