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The Law of Cosines

This lesson features a second formula that helps to solve triangles. Sine Law, which is part of the CST 10 curriculum, offers us a way to solve triangles when sides and their corresponding angles (opposite angle) are given. However, what happens when there are two sides in a triangle and the enclosed angle between them? What about when you are given three sides and no angles? How do you solve these kinds of triangles? In this lesson, students are introduced to cosine law, which enables you to solve these special cases.

Learning Goals:

  • To find unknown measures in any triangle using the cosine law
Related Textbook Pages:

VisionsScience, Student Book Volume 2, Secondary Cycle TwoYear Two,  Les Editions CEC inc,  2009, pp 180-193

Additional Resources:
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