# Law of Cosines

1.   $\rhd$ Solving for a side of the triangle with the law of cosines. (4:38)
Side $b$ of a triangle is 12 and side $c$ of a triangle is 9, and the angle contained between them is 87 degrees.  What is the length of the other side of the triangle? Solution: $a \approx 14.62$
2.   $\rhd$ Solving for an angle with the law of cosines. (6:41)
Given a triangle with base 60 $m$ and other sides 50 $m$ and 20 $m$, find the angle $\theta$ between the base and the longer side of the triangle. Solution: $\theta \approx 18.19$ degrees.
3.   $\star$ Solve a triangle using the law of cosine
4.   $\rhd$ Proof of the law of cosines (9:26)