Education Technology

Geometry: Angle-Side Relationships

by Texas Instruments


  • Students will recognize that the largest angle in a triangle is opposite the largest side, the second largest angle is opposite the second largest side, and the smallest angle is opposite the smallest side.
  • Students will recognize that given three segments and three angles that form a triangle, the triangle will be unique.


  • opposite sides
  • opposite angles

About the Lesson

This lesson involves students manipulating three segments and three angles to build a triangle. As a result students will:

  • Attach an angle to the longest segment; discover that the largest angle cannot be attached to the longest side to form a triangle.
  • Build a triangle starting with the largest angle; discover there are restrictions on which side has to be opposite which angle.
  • Recognize and generalize the relationship between the sides and the angles in a triangle.