The Law of Cosines is a helpful tool in certain situations. Let’s break it down:

1. When You Have Two Sides and the Angle Between Them (SAS):
   If you know the lengths of two sides and the angle that’s between them, you can use the Law of Cosines to find the length of the third side.

   • For example, if you know sides ( a ) and ( b ), and the angle ( C ), you can find side ( c ) using this formula:
     [ c^2 = a^2 + b^2 - 2ab \cdot \cos(C) ]

2. When You Know All Three Sides (SSS):
   If you have the lengths of all three sides, you can use the Law of Cosines to figure out the angles.

   • For example, to find angle ( C ), you can use this formula:
     [ \cos(C) = \frac{a^2 + b^2 - c^2}{2ab} ]

Remember, if you have angles and the sides that are not between them, you should use the Law of Sines instead!