Central angle intersection points and of the legs of the angle with the circle form a diameter, then is a straight angle. (In radians, .) Let be the minor arc of the circle between points and , and let be the radius of the circle. If the central angle is subtended by , then If the central angle is not subtended by the minor arc , then is a reflex angle and If a tangent at and a tangent at intersect at the exterior point , then denoting the center as , the angles (convex) and are supplementary (sum to 180°). A
Angle C, and ∠CAB to the anticlockwise (positive) angle from C to B. The names, intervals, and measured units are shown in a table below: When two straight lines intersect at a point, four angles are formed. Pairwise these angles are named according to their location relative to each other. A transversal is a line that intersects a pair of (often parallel) lines and is associated with "alternate interior angles", "corresponding angles", "interior angles", and "exterior angles". There are three special angle pairs which involve the summation of angles: The size of a geometric angle is usually characterized by the magnitude