THEOREM OF THE DAY: al-Kashi’s Law of Cosines

If $A$ is the angle at one vertex of a triangle, $a$ is the opposite side length, and $b$ and $c$ are the adjacent side lengths, then 

$a ^2 = b ^2 + c ^2 − 2bc cos A$.

Κάντε κλικ στην εικόνα.