Khan Academy
Khan Academy: Trigonometry: Proof: Law of Sines
Video deriving the law of sines. Includes discussion of why it is useful. [6:33]
Virtual Nerd
Virtual Nerd: What Is the Law of Cosines?
The Law of Cosines helps solve some triangle problems. This video explains several versions of the law of cosines and what they are used for. [9:22]
Sophia Learning
Sophia: Solving an Sas Triangle With the Law of Cosines: Lesson 1
Solving an SAS by using the Law of Cosines is demonstrated here. This lesson is 1 of 6 in the series titled "Solving an SAS Triangle with the Law of Cosines." [3:22]