Step 1: Remember the law of sine and law of cosines formulas and properties.

Link: http://mathematics.laerd.com/maths/trigonometry-sine-and-cosine-rules-intro.php

Step 2: Look at the given measurements and identify the suitable law for the question.

NOTE:If you know the lengths of all three sides (like a, b, and c).

First, use the Law of Cosines to solve for the cosine of an angle.

Then, use the inverse cosine function to solve for the measure of that

angle.

EXAMPLE: You know all three side lengths, so you can use the

Law of Cosines to find the measures of any of the angles.

q^2 = r^2 + s^2 - 2rs cos(Q)

Since you don't know any angles, you can't start with the Law of Sines.