What defines an acute angle?

An acute angle is defined as an angle that measures less than 90 degrees. This means that any angle that falls within this range, from 0 degrees up to but not including 90 degrees, qualifies as acute.

The characteristics of acute angles are significant in geometry, especially when understanding the classification of angles based on their degree measures. Understanding acute angles allows for a deeper grasp of various geometric concepts, such as triangle types, where acute angles are present in acute triangles.

In contrast, options that suggest the angle is equal to 90 degrees, greater than 180 degrees, or specifically equal to 45 degrees do not align with the definition of an acute angle. The definitions of a right angle and obtuse angle cover those cases, while the specific measure of 45 degrees, while it is an acute angle, does not encompass the broader definition that any measure less than 90 degrees would provide.