Lesson 3

Lesson 3 Summary

 

In this lesson you learned that although the sine law is valid for all triangles, sometimes the information that you are given is not enough to use the sine law.

 

You also learned the cosine law, which is valid for all triangles (just like the sine law):

 

a2 = b2 + c2 − 2bc cos A

 

 

When deciding whether to use the sine law or the cosine law, consider which values are given and which values you need to find. If you have a side-angle pair (i.e., one side and its opposite angle), then you can use the sine law. If you do not have a side-angle pair, then you will likely need to use the cosine law.

 

In the next lesson you will apply what you have learned about the sine and cosine laws to problems involving more than one triangle.