Final answer:
An exterior angle of a triangle is supplementary, not complementary, to its adjacent interior angle, as their sum equals 180 degrees.
Step-by-step explanation:
An exterior angle of a triangle is not complementary to its adjacent interior angle. Instead, the exterior angle is supplementary to the adjacent interior angle, meaning their sum is 180 degrees. This is because each angle in a triangle adds up to 180 degrees, and the exterior angle alongside the interior angle form a straight line when extended outside of the triangle, which is by definition a 180-degree angle.
For example, if you have a triangle with angles measuring 50 degrees and 60 degrees, the third angle would measure 70 degrees (because 50 + 60 + 70 = 180). The exterior angle adjacent to this 70-degree angle would measure 110 degrees, since 110 + 70 = 180.
In general, the relationship between an interior angle and its corresponding exterior angle in a polygon is one of supplementary angles, not complementary. Complementary angles are two angles that add up to 90 degrees.