Section 6.5 Law of Cosines Objectives:

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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.

Law of Cosines:

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

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

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

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

EX 4. Solve for x.

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)

Heron’s Formula:

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