At what angle measure is a right angle?

A right angle is defined as an angle that measures exactly 90 degrees. This measurement is universally recognized in geometry and is foundational in various mathematical applications, such as in the definition of perpendicular lines. When two lines intersect at a right angle, they create four angles that are all equal to 90 degrees.

The characterization of right angles is fundamental in both theoretical and applied mathematics, including architecture, engineering, and various fields where angles play a crucial role. The other angle measures provided do not represent right angles: 45 degrees is an acute angle, 180 degrees is a straight angle, and 360 degrees corresponds to a full rotation. Thus, the choice of 90 degrees unmistakably defines a right angle.