The document discusses the Law of Cosines, which is an equation used to solve for unknown sides and angles of triangles when certain information is known. It states that the Law of Cosines can be used when two sides and the included angle are known (SAS) or when all three sides are known (SSS). It then provides two examples of using the Law of Cosines to solve for a missing side length or angle measure.

1. Law of Cosines May 11, 2011
12‐4 The Law of Cosines
Objectives:
1. To use Law of Cosines to solve triangles
2. To solve problems by using the Law of Cosines
Let ∆ABC be any triangle with a, b, & c representing the measures of sides
opposite angles A, B, & C, respectively. Then the following equation is true:
C
2 2 2
a = b + c - 2bc cosA a
b
A c B
HW Law of Cosines Wkst 1

2. Law of Cosines May 11, 2011
When do we use Law of Cosines??????
Case 1: When you know 2 sides & the included angle (SAS)
What it looks like . . .
Case 2: When you know all 3 sides (SSS)
What it looks like . . .
HW Law of Cosines Wkst 2

3. Law of Cosines May 11, 2011
Find a if c = 8, b = 10, and m∠A = 60.
In a ∆QRS, q = 37, r = 23, and s = 18.
Find the measure of ∠R.
HW Law of Cosines Wkst 3

4. Law of Cosines May 11, 2011
HW: Wkst
HW Law of Cosines Wkst 4