1. Law of Cosines

2. We use the law of cosines and the law of sines because we need to be able to find missing sides and angles of triangles when they are not right triangles. When we had right triangles, we used SOH-CAH-TOA or the Pythagorean Theorem. Now we need another way to find these sides and angles. First, we need to learn how to label a triangle: A B C a b c Notice that the side is labeled with the lower case letter of the angle across from it! Remember: 1.The largest side of a triangle is across from the largest angle 2.The smallest side is across from the smallest angle.

3. When using the law of cosines, draw a picture first, then plug into the formula! A B C a b c When looking for a side, you need the angle across from the side and the other two sides. Notice that the letter in front must match the letter in the back!

4. A B C 12.4 a

5. M N P 120 5.8 8.3 n

6. A B C 15.3 7.1 9.4

7. A B C 12 8 5

8. Homework Page 1 #6,7,9