Course: Trigonometry
Topic: Oblique Triangles and the Laws
Subtopic: Law of Sines


All the trig we have done so far in the course has been "right angle trig" where we required a right triangle before we could set-up and use any of the six trig functions. In this chapter we learn two laws that enable us to use trig functions on oblique (non-right) triangles. The first of these is the law of sines. It is based on ratios of the sine of an angle and the length of the side opposite that angle.


By the end of this topic you should know and be prepared to be tested on:


Terms you should be able to define: oblique triangle, included side, law of sines

Memorize the Law of Sines! All variations on the proportions are shown below using standard triangle notation. Note that you can "flip" all three ratios if you need the side variables in the numerator instead.

Mini-Lectures and Examples

STUDY: Oblique Triangles - Law of Sines & the Ambiguous Case

Supplementary Resources

Need help understanding how to identify AAS, ASA, etc.? Read Help for Oblique Triangles.

rev. 2020-11-05