1. The Cosine Rule A B C a b c

2. The Cosine Rule A B C a b c

3. A B C a b c

4. When To Use The Cosine Rule. The Cosine Rule can be used to find a third side of a triangle if you have the other two sides and the angle between them. 6 10 65 o L89 o 13.8 6.2 W 147 o 8 11 M

5. Calculating Sides Using The Cosine Rule(1). Calculate the length AC 30m 55° 40m

6. 30m 55° 40m b a c

8. Calculating Sides Using The Cosine Rule(2). Calculate the length CB 100 ° 13cm 5cm

9. 100 ° 13cm 5cm b a c

11. Rearranging the cosine rule. You now have a formula for finding an angle if you know all three sides of the triangle.

12. Calculating Angles Using The Cosine Rule (1). Calculate the angle CAB

13. b a c ?

15. Calculating Angles Using The Cosine Rule (2). Calculate the angle ?

16. B A C b a c