Answer:
Identify angle C. It is the angle whose measure you know.
Identify a and b as the sides that are not across from angle C.
Substitute the values into the Law of Cosines.
Solve the equation for the missing side.
Explanation:
For a right triangle, use the Pythagorean Theorem. For an isosceles triangle, use the area formula for an isosceles. If you know some of the angles and other side lengths, use the law of cosines or the law of sines.