The Angle-Angle (AA) Criterion for Two Triangles to Be Similar

What do you need to prove triangles are similar? Learners answer this question through a construction exploration. Once they establish the criteria, they use the congruence and proportionality properties of similar objects to find missing sides. 

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CCSS: Designed
Instructional Ideas

  • Incorporate modalities such as ang-legs for exploration in place of the constructions
  • Provide non-examples of similar triangles to allow for comparison
Classroom Considerations

  • Opening activity requires construction tools
  • Pupils must be able to solve proportions; review as necessary
  • The lesson continues from the first fourteen in a 36-part series
Pros

  • Takes a hands-on approach to determine criterion for similar triangles
  • Questioning encourages critical thinking
Cons

  • None