Law of Sines Basics

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SWBAT use the Law of Sines to solve oblique triangles.

Big Idea

This direct instruction lesson introduces basic cases of the Law of Sines.


5 minutes

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.  

Explanation: Law of Sines

40 minutes

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:

Law of Sines

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.

Closure: 3W's

5 minutes

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.


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.