A 90? angle. The third of the four angles below is a right angle. The first two are obtuse angles. The last is an acute angle.Perpendicular lines or edges are at right angles to each other. The corners of every square and rectangle are right angles. Sheets of paper are cut, and moldings for picture frames are mitered so that their corners are right angles. A typical cross is formed by the intersection of two line segments at right angles to each other.