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# Law of Sines Basics

Lesson 9 of 17

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

*50 minutes*

#### Warm-up

*5 min*

There is a warm-up question on page 1 of today’s PowerPoint Law of Sines PowerPoint. The task gives students a relatively straight-forward chance to practice modeling and solving a problem with right triangle trigonometry. When reviewing this warm-up question with my students, I make sure to emphasize the idea that we are assuming that this situation can be modeled with a right triangle. Today, we will move on and explore how to solve problems when we cannot make this assumption.

#### Resources

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#### Explanation: Law of Sines

*40 min*

To introduce students to the Law of Sines, I decided that direct instruction would be best. I haven’t thought of a good way yet to guide my students to developing this knowledge on their own. My lesson plan employs a PowerPoint presentation as a core resource:

I will begin by first discussing the fact that the Law of Sines can be used to solve oblique triangles. Then, I will present the examples on slides 5-8 of the PowerPoint with students following along. Students will have a chance to practice on their own on slide 9. Slides 10-17 walk students through how to completely solve a triangle using the Law of Sines. Slide 18 will be an opportunity for individual practice.

If there is time available, I will present the example on slides 19-21. If not, I will skip to the final slide, #22, and have students try a problem in context.

#### Resources

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#### Closure: 3W's

*5 min*

To close this lesson, I will give students a few minutes to discuss the Law of Sines and their application in teams. When they finish their discussion, I will ask each student to share out their 3 W's for me to review.

#### Resources

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Today, I will give Homework 6 - Fundamentals of Trigonometry to students to give them the opportunity to apply the information about the Law of Sines that was shared in class today.

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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