Geometry/Angles < Geometry This page may need to be reviewed for quality. An angle is the union of two rays with a common endpoint, called the vertex. The angles formed by vertical and horizontal lines are called right angles; lines, segments, or rays that intersect in right angles are said to be perpendicular. Angles, for our purposes, can be measured in either degrees (from 0 to 360) or radians (from 0 to ). Angles length can be determined by measuring along the arc they map out on a circle. In radians we consider the length of the arc of the circle mapped out by the angle. Since the circumference of a circle is , a right angle is radians. In degrees, the circle is 360 degrees, and so a right angle would be 90 degrees. Contents [hide ] 1 Naming Conventions 2 Classification of Angles by Degree Measure 3 Special Pairs of Angles 4 Navigation Naming Conventions[edit ] Angles are named in several ways. By naming the vertex of the angle (only if there is only one angle formed at that vertex; the name must be non-ambiguous) By naming a point on each side of the angle with the vertex in between. By placing a small number on the interior of the angle near the vertex. Classification of Angles by Degree Measure[edit ] Acute Angle an angle is said to be acute if it measures between 0 and 90 degrees, exclusive.
