Education Technology

Precalculus: Law of Sines
by Texas Instruments

Published on August 10, 2011


  • Students will understand how the Law of Sines is derived.
  • Students will understand when the Law of Sines can be used to find missing sides and angles in a triangle.
  • Students will be able to solve for missing sides and angles in a triangle using the Law of Sines, when appropriate.


  • sine of an angle
  • obtuse angle
  • acute angle
  • right angle
  • Ambiguous Case of the Law of Sines

About the Lesson

This lesson involves exploring the relationship known as the Law of Sines.
As a result, students will:

  • Manipulate a triangle to observe the equality of ratios of side lengths and sines of opposite angles.
  • Manipulate a triangle to decide when the Law of Sines gives an unambiguous result.
  • Consider the Law of Sines in connection with previous knowledge about right triangle trigonometry.
  • Determine when the Law of Sines can be used to solve for unknown side lengths and angle measures in a triangle, and apply it to solve when possible.