Law of Cosines: Given three sides

Example:
In triangle ABC, a = 9 cm, b = 10 cm and c = 13 cm. Find the size of the largest angle.

Solution:
The largest angle is the one facing the longest side, i.e. C.

c² = a² + b² – 2ab cos C

= 0.067

∠C = 86.2°

How to use the cosine rule?
One given SAS and the other given SSS.
Using Law of Cosines to solve triangles given 3 sides (SSS) and 2 sides and the angle in between (SAS).