What do you call an angle formed when lines extend in opposite directions from a point?

An angle formed when lines extend in opposite directions from a point is called a straight angle. A straight angle measures exactly 180 degrees, which represents a straight line. This occurs when two rays (or lines) originate from a common point and extend outwards in opposite directions, creating a straight path.

Understanding straight angles is fundamental in geometry, as they serve as a basis for identifying other types of angles and their relationships. Supplementary angles, on the other hand, are two angles that add up to 180 degrees, but they do not need to be formed in the manner described in the question. Complementary angles add up to 90 degrees and are not relevant here. Acute angles measure less than 90 degrees, which also does not apply to the scenario presented. Thus, the concept of a straight angle accurately captures the situation described in the question.