Trigonometric Identities and Equations

Lesson 16

Math

Unit 7

11th Grade

Lesson 16 of 16

Objective


Find missing side lengths and angle measures using the Law of Cosines in acute triangles.

Common Core Standards


Core Standards

  • G.SRT.D.10 — Prove the Laws of Sines and Cosines and use them to solve problems.

Criteria for Success


  1. Derive the Law of Cosines.
  2. Identify when the Law of Cosines can be applied to triangles.
  3. Apply the Law of Cosines to identify missing angles in a triangle.
  4. Apply the Law of Cosines to identify a missing side in a triangle.
  5. Apply the Law of Cosines with word problems. 
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Anchor Problems

25-30 minutes


Problem 1

The Law of Cosines states:

What measurements of a traingle make the most sense to use the Law of Cosines?

Guiding Questions

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Problem 2

Would you use Law of Sines, Law of Cosines, or Pythagoream Theorem to find the value of $$x$$?

Guiding Questions

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References

EngageNY Mathematics Geometry > Module 2 > Topic E > Lesson 33Opening Exercise

Geometry > Module 2 > Topic E > Lesson 33 of the New York State Common Core Mathematics Curriculum from EngageNY and Great Minds. © 2015 Great Minds. Licensed by EngageNY of the New York State Education Department under the CC BY-NC-SA 3.0 US license. Accessed Dec. 2, 2016, 5:15 p.m..

Modified by Fishtank Learning, Inc.

Target Task

5-10 minutes


Use the Law of Cosines to find the solution to the following problem. 

Your school is challenging classes to compete in a triathlon. The race begins with a swim along the shore and then continues with a bike ride for $$4$$ miles. School officials want the race to end at the place it began, so after the $$4$$-mile bike ride, racers must turn $${30^{\circ}}$$ and run $${3.5}$$ miles directly back to the starting point. What is the total length of the race? Round your answers to the tenths place.

References

EngageNY Mathematics Geometry > Module 2 > Topic E > Lesson 33Exercise #2

Geometry > Module 2 > Topic E > Lesson 33 of the New York State Common Core Mathematics Curriculum from EngageNY and Great Minds. © 2015 Great Minds. Licensed by EngageNY of the New York State Education Department under the CC BY-NC-SA 3.0 US license. Accessed Dec. 2, 2016, 5:15 p.m..

Modified by Fishtank Learning, Inc.

Additional Practice


The following resources include problems and activities aligned to the objective of the lesson that can be used for additional practice or to create your own problem set.

  • Include mixed practice between Law of Cosines and Law of Sines.
  • Include nonexamples where there is not enough information to solve the triangle. 
  • Include a mix of contextual and noncontextual problems.

Lesson Map

A7CB09C2-D12F-4F55-80DB-37298FF0A765

Topic A: Basic Trigonometric Identities and Equivalent Expressions

Topic B: Solve Trigonometric Equations

Topic C: Advanced Identities and Solving Trigonometric Equations

Topic D: Applications and Extensions of Trigonometric Functions

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