1. Law of Cosines Use it when you are given Side-Side-Side (SSS) or Side-Angle-Side (SAS)

2. Law of Cosines

3. Another form of the formula

4. Example 1 Find the three angles of the following triangle (Hint: Find the largest angle first) A B C b= 19 ft a = 8 ft c=14 ft

5. This is why you should find the largest angle first……… Cos ϑ >0 for 0°< ϑ <90°Acute Cos ϑ <0 for 90° < ϑ < 180 ° Obtuse

6. Find the remaining angles and side of the triangle…. A B C b= 15 cm a c=10 cm

7. The pitcher’s mound on a women’s softball field is 43 feet from home plate and the distance between the bases is 60 feet, (the pitcher’s mound is not halfway between home plate and second base.) How far is the pitcher’s mound from first base? H = 45° h f = 43 ft P p = 60 ft

8. A ship travels 60 miles due east, then adjusts its course northward. After traveling 80 miles in that direction, the ship is 139 miles from its point of departure. Describe the bearing from point B to point C. A B C b = 139 mi a = 80 mi c = 60 mi

9. Heron’s Formula, s = the perimeter divided by 2

10. Find the area of the triangle having sides of lengths a = 43 meters, b = 53 meters, and c = 72 meters

11. Class work

12. Homework Pg. 595: 2-10 even, 24, 26