What is a straight angle defined as?

A straight angle is defined as an angle that measures exactly 180 degrees. This means that it forms a straight line, effectively dividing a plane into two equal halves. In geometry, angles are classified based on their measures, and a straight angle is a fundamental concept that represents a straight line rather than a conventional angle.

In contrast, the other options present different types of angles: an angle that measures more than 180 degrees is considered a reflex angle, while one that measures exactly 90 degrees is a right angle, and an angle that measures less than 90 degrees is known as an acute angle. Thus, the definition of a straight angle as measuring 180 degrees is essential for understanding the classification and properties of angles in geometry.