SOHCATOA cosine law Archives - Math and Multimedia

An elementary proof of the cosine law

April 12, 2011 GB High School Geometry, High School Mathematics, High School Trigonometry, Problem Solving and Proofs

The cosine law states that in triangle $ABC$ with side lengths $a, b,$ and $c$ , the following equations are satisfied:

$a ^2 = b^2 + c^2 - 2bc$ $\cos A$ *

$b ^2 = a^2 + c^2 - 2ac$ $\cos B$

$c ^2 = a^2 + b^2 - 2ab$ $\cos C$

The discussion below shows how these equations were derived. » Read more

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