1. Section 9.3
The Law of Sines
Objective:
Use the Law of Sines to find unknown parts
of triangles.
A
B
C

2. Law of Sines
C
Use our new formula to
find the area of this
triangle three different
ways.
B A
Divide all three sides by 1wabc to get:
Law of Sines

3. Law of Sines
C
A = 40° Solve the
C = 60° triangle.
a = 10
B A
Answers

4. Law of Sines
C
A = 35° Solve the
C = 70° triangle.
b = 12
B A
Answers

5. Law of Sines
In the first example, we knew AAS about our
triangle.
In the second example, we knew ASA about
our triangle.
What other combinations of sides and angles
completely specify a triangle?

6. Law of Sines
C
B = 30° Solve the
a = 10 triangle.
b=4
B A
Answers

7. Law of Sines
C
B = 30° Solve the
a = 10 triangle.
b=4
B A
What is the problem here?

8. Law of Sines
C
B = 30° Solve the
a = 10 triangle.
b=4
B A
What is the problem here?

9. Law of Sines
C
B = 30° Solve the
a = 10 triangle.
b=4
B A
What is the problem here?