1. Chapter 9 Law of Cosines and Law of Sines
Concept #1 The Law of Cosines is used when a triangle has a SSS or a SAS situation . ( This idea was used in proving triangle congruence. Now we use it to analyze which law should be used to solve a triangle. ) Use the law twice always 𝑎 2 = 𝑏 2 + 𝑐 2 −2𝑏𝑐𝐶𝑜𝑠𝐴 𝑏 2 = 𝑎 2 + 𝑐 2 −2𝑎𝑐𝐶𝑜𝑠𝐵 𝑐 2 = 𝑎 2 + 𝑏 2 −2𝑎𝑏𝐶𝑜𝑠𝐶

2. Use this triangle A b a c B C

3. Problem #1
Solve the triangle Given
𝑎=20 𝑏=30 𝑐=42

4. Problem #1
Solve the triangle Given
𝑎=20 𝑏=30 𝑐=42

5. Problem #2
Solve the triangle Given
𝑎=11 ∠𝐵= 22 ∘ 𝑐=16

6. Problem #2
Solve the triangle Given
𝑎=11 ∠𝐵= 22 ∘ 𝑐=16

7. Concept #2 Law of Sines
The Law of Sines is used when a triangle has a ASA or a AAS situation . Use the law twice always 𝑎 𝑠𝑖𝑛𝐴 = 𝑏 𝑠𝑖𝑛𝐵 = 𝑐 𝑠𝑖𝑛𝐶

8. Problem #3
Solve the triangle Given
𝑎=11 ∠𝐵= 22 ∘ ∠𝐶= 77 ∘

9. Problem #3
Solve the triangle Given
𝑎=11 ∠𝐵= 22 ∘ ∠𝐶= 77 ∘

10. Problem #4
Solve the triangle Given
b=71 ∠𝐵= 34 ∘ ∠𝐶= 100 ∘

11. Problem #4
Solve the triangle Given
b=71 ∠𝐵= 34 ∘ ∠𝐶= 100 ∘

12. H.W. Law of sine and cosine Worksheets