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# Law of Cosines

Lesson 11 of 17

## Objective: SWBAT use the Law of Cosines to solve oblique triangles.

*50 minutes*

#### Warm-up

*10 min*

The warm-up question for today is located on Slide 1 of the PowerPoint Law of Cosines.

I want my students to continue to practice the ambiguous case of the Law of Sines by determining how many triangles would be created given each situation. Once we review the Law of Sines, I will connect this to the Law of Cosines. It is essential that students see that the Law of Sines cannot be used to solve all oblique triangles as we always need an angle and side pair. I want students to understand why these two Laws are necessary.

#### Resources

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At the conclusion of this lesson, students have been exposed to all the major learning in this unit. So it is a great time for them to complete a 3-2-1 Assessment based on this Unit. Their responses can help us judge what to focus on during the review day this unit.

#### Resources

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Tonight my students will begin to work on Homework 7 - Fundamentals of Trigonometry. The assignment provides the students with a lot of practice with the Laws of Sine and Cosine.

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- UNIT 1: Basic Functions and Equations
- UNIT 2: Polynomial Functions and Equations
- UNIT 3: Rational Functions and Equations
- UNIT 4: Exponential Functions and Equations
- UNIT 5: Logarithmic Functions and Equations
- UNIT 6: Conic Sections
- UNIT 7: Rotations and Cyclical Functions
- UNIT 8: Cyclical Patterns and Periodic Functions
- UNIT 9: Trigonometric Equations
- UNIT 10: Matrices
- UNIT 11: Review
- UNIT 12: Fundamentals of Trigonometry

- LESSON 1: What's so special about similar right triangles?
- LESSON 2: Calculator Investigation: Special Right Triangles (Day 1 of 2)
- LESSON 3: Calculator Investigation: Special Right Triangles (Day 2 of 2)
- LESSON 4: Using Trigonometric Ratios (Day 1 of 2)
- LESSON 5: Using Trigonometric Ratios (Day 2 of 2)
- LESSON 6: Clinometer Project (Day 1 of 2)
- LESSON 7: Clinometer Project (Day 2 of 2)
- LESSON 8: Applications of Right Triangle Trig
- LESSON 9: Law of Sines Basics
- LESSON 10: Ambigouous Cases of the Law of Sines
- LESSON 11: Law of Cosines
- LESSON 12: Short Lesson: Quick Clicker Quizzes
- LESSON 13: More on the Laws: Real World Application
- LESSON 14: Trig Jeopardy
- LESSON 15: Fundamentals of Trig Review - Day 1 of 2
- LESSON 16: Fundamentals of Trig Review - Day 2 of 2
- LESSON 17: Fundamentals of Trigonometry Unit Assessment