Answer
We use the law of cosines to find the missing parts of triangles for which we are given two $sides$ and the $angle$ between them, or for which we are given all three $sides$. In either case, a $unique$ triangle is determined.
Work Step by Step
As per the law of cosines, we have,
$a^{2}=b^{2}+c^{2}-2bc(cosA)$
So, if we know two sides and the angle between them, we can find all measurements of the triangle.
Also, when all three sides are given, the angles can found out by this law, and the triangle is unique.
