Law of Cosines

Move the vertices to set up your problem, then step through the solution process.
Try to discover the formula and determine if it would work in solving for the other angles or sides.

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Notice that the Law of Sines works for known Side-Angle-Side (SAS).
If you have a known Side-Side-Side (SSS) problem, you can use the same equation, just
solving for one of the ANGLES, instead.

In short, the Law of Cosines requires either SAS or SSS knowledge.

The Law of Cosines is a generalization of the Pythagorean Theorem. When A is a right angle, cos A = 0, and the formula devolves into the Pythagorean Thereom: a² = b² + c².

Mark Fowler, Grafton HS, Created with GeoGebra