A Different Proof of the Law of Cosines

Build upon the Pythagorean Theorem with the Law of Cosines. The 10th part of a 16-part series introduces the Law of Cosines. Class members use the the geometric representation of the Pythagorean Theorem to develop a proof of the Law of...

Use the Law of Cosines and the Law of Sines to solve problems using the sums of vectors. Pupils work on several different types of real-world problems that can be modeled using triangles with three known measurements. In the process,...

Laws are meant to be broken, right? Learners derive the Law of Sines by dropping a perpendicular from one vertex to its opposite side. Using the Law of Sines, mathematicians solve for various parts of triangles.

Sal derives the Law of Cosines using a method similar to the wayward ship captain word problem he solves in another video. This video provides a good review of using the SOH-CAH-TOA model, the Pythagorean Theorem, some of the basic trig...

In this video, Sal proves the Law of Sines by using the SOH-CAH-TOA model and setting up equivalent ratios.

Explore triangle problems that require the Law of Sine or Law of Cosine. A straightforward lesson focuses on deciding when to use each law. The instructor presents several triangles for pupils to consider and describes patterns in the...

Your class knows the Pythagorean Theorem, but can they prove it? A series of three videos shows two proofs of the Pythagorean Theorem and use it to classify triangles. 

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...

This tutorial examines the law of sines and the law of cosines. Includes class notes, examples, and a variety of practice problems with solutions. The teacher resource consists of a lab that utilizes the law of sines and the law of cosines.

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.