Final answer:
When given a 120-degree exterior angle of a triangle with two equal interior opposite angles, each of those interior opposite angles measures 60 degrees, using the property that the sum of the interior angles of a triangle is 180 degrees.
Step-by-step explanation:
The question is about finding the measure of the interior opposite angles of a triangle when given the measure of an exterior angle that is 120 degrees. Knowing that the sum of an exterior angle and its adjacent interior angle is 180 degrees, we can determine that the adjacent interior angle to the 120-degree exterior angle is 60 degrees. Since it's given that the two interior opposite angles are equal, we utilize the fact that the sum of angles in any triangle is 180 degrees. Subtracting the known 60-degree angle from 180 degrees leaves us with 120 degrees. Divide this by 2, as the remaining two angles are equal, and we find that each of these angles measures 60 degrees.