Law of Cosines

Build upon the Pythagorean Theorem with the Law of Cosines. The 10th part of a 16-part series introduces the Law of Cosines. Class members use the the geometric representation of the Pythagorean Theorem to develop a proof of the Law of Cosines. Pupils apply what they learned and use the Law of Cosines to find measurements in oblique triangles.

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CCSS: Designed
Instructional Ideas

  • Have the class determine the range of the length of the third side
  • Create pairs and have them create problems that require them to apply the Law of Cosines to solve
Classroom Considerations

  • Class members should be familiar with the geometric representation of the Pythagorean Theorem
Pros

  • Scaffolding gives the teacher hints where the class may make common mistakes
  • Resource uses colors to distinguish the different geometric figures
Cons

  • None
Common Core