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
Antiparallel (mathematics) and only if they make the same angle formula_18 in the opposite senses with the bisector of that angle (Fig.3). In a Euclidean space, two directed line segments, often called "vectors" in applied mathematics, are antiparallel, if they are supported by parallel lines and have opposite directions. In that case, one of the associated Euclidean vectors is the product of the other by a negative number. Antiparallel (mathematics) In geometry, anti-parallel lines can be defined with respect to either lines or angles. Given two lines formula_1 and formula_2, lines formula_3 and formula_4 are anti-parallel with respect to formula_1 and formula_2