Education Technology

# Law of Cosines

Math: Precalculus: Trigonometric Laws and Identities
9-12
45 Minutes
TI-Nspire™ CX/CX II
TI-Nspire™ CX CAS/CX II CAS
TI-Nspire™
TI-Nspire™ CAS
3.2
Lessons
TNS

# Law of Cosines

Activity Overview

This lesson involves visualizing and exploring the Law of Cosines.

Objectives

• Students will be able to state the Law of Cosines.
• Students will be able to apply the Law of Cosines to find missing sides and angles in a triangle.
• Students will understand why the Law of Cosines is true.

Vocabulary

• cosine of an angle
• obtuse angle
• acute angle
• right angle

This lesson involves visualizing and exploring the Law of Cosines.
As a result, students will:

• Manipulate a triangle to observe the equality of the Law of Cosines.
• Manipulate a triangle to discover why the Law of Cosines is true.
• Consider the Law of Cosines in connection with previous knowledge about right triangle trigonometry.
• Determine when the Law of Cosines can be used to solve for unknown side lengths and angle measures in a triangle, and apply it to solve when possible.