Wolfram Research
Wolfram Math World: Law of Cosines
This page from MathWorld.com gives a good explanation of the Law of Cosines, which relates the lengths of the legs of a triangle to the angles. This site shows how the formula is derived, along with a triangle to clarify variables. Also...
Other
Trig Without Tears: Solving Triangles
This page provides a good explanation of how to solve oblique triangles (triangles containing no right angles.) The Law of Cosines section is about halfway of the way down the page.
Georgia State University
Georgia State University: Hyper Physics: Law of Cosines
This page from the Georgia State University provides a definition of the Law of Cosines. Also includes a "calculator" to help you find side lengths and opposite angles when you are given either three sides or two sides and a third angle.
Cut the Knot
Cut the Knot!: The Law of Cosines (Cosine Rule)
This site from Cut The Knot provides an overview of the law of cosines, complete with an explanation of the law and a proof of the law.
Oswego City School District
Regents Exam Prep Center: Working on a Rescue Team Lab
Your students are part of the Yellowstone National Park rescue team which has just been dispatched to help located a downed plane. How can they effectively use the Law of Sines and the Law of Cosines to assist them in finding the plane?...