Education Technology

Geometry: Trig Ratios
by Texas Instruments

Updated on December 12, 2014


  • Students will identify the effects of changing the sides and angles on the sine, cosine, and tangent ratios.
  • Students will apply the properties of similar triangles to develop the definitions of trigonometric ratios in right triangles.
  • Students will connect the terms sine, cosine, and tangent with appropriate ratios in a right triangle.
  • Students will construct arguments and defend their reasoning with mathematical examples and counterexamples.


  • sine
  • cosine
  • tangent
  • adjacent leg
  • opposite leg
  • hypotenuse
  • similar right triangles

About the Lesson

This lesson involves manipulating the angles and sides of a right triangle. As a result, students will:

  • Observe the conditions under which the ratio does not change.
  • Define the trigonometric ratios of sine, cosine, and tangent.