Cosine theorem?

this formula is used in triangles to define either a cosine or the side of the triangle opposite of the cosine's angle

c²=a²+b²-2abcosc

cosc= the cosine of the angle opposite of the c side of the triangle ABC

hence cosc=(a²+b²-c²)/2ab hereby the same is true for cosa where cosa is the cosine of the angle opposite of the a side and for cosb where cosb is the cosine of the angle opposite of the side b in the triangle