Math 300, Spring 2003

John Baldwin

Law of Cosines

The Law of Cosines states that if the three sides of a triangle have lengths a, b and c and if g is the angle opposite the side of length c, then c² = a² + b² – 2ab cosg. In the special case that g is a right angle we obtain as a corollary the Pythagorean Theorem: c² = a² + b².