Introduce Special Right Triangles

  1. Introduce 45-45-90 and 30-60-90 triangles, along with formulas.  Use real-world examples or pictures with angles and one side given, and then ask students to find one of the two other sides.
  2. Show students how to prove the Pythagorean identity and use it to find sin, cos, and tan.
  3. Establish the criteria for two triangles to be similar.

Tips and Tools

Have students use Sketchometry or Geometer’s Sketchpad. Both are tools for use with geometry.

Use these Khan Academy tutorials on the special properties and parts of triangles.

Highlight Mathematical Practice 4. What examples of geometry or right triangles do they observe in the real world examples?