CPM Homework Help : CCA2 Problem 12-120

If the side lengths of $∆ABC$ are $a = 9$ , $b = 10$ , and $c = 5$ , calculate the measure of the largest angle.

Hint:

Start by drawing a triangle and labeling the sides and angles.
Use the Law of Cosines, then Law of Sines to calculate the measures of the angles.
Which angle is the largest?