Law Of Cosines

The Pythagorean Theorem for right triangles can be generalized to apply to oblique triangles as well. For a triangle with angles $\alpha,\;\beta,\;\gamma$ and respective opposite sides $a,\;b,\;c\;:$

$\displaystyle a^2$	$\displaystyle = b^2+c^2-2bc \cos\alpha$
$\displaystyle b^2$	$\displaystyle = a^2+c^2-2ac \cos\beta$
$\displaystyle c^2$	$\displaystyle = a^2+b^2-2ab \cos\gamma$