In geometry, an angle is subtended by an arc, line segment or any other section of a curve when its two rays pass through the endpoints of that arc, line segment or curve section. Conversely, the arc, line segment or curve section confined within the rays of an angle is regarded as the corresponding subtension of that angle. We also sometimes say that an arc is intercepted or …

Angle trisection is a classical problem of straightedge and compass construction of ancient Greek mathematics.It concerns construction of an angle equal to one third of a given arbitrary angle, using only two tools: an unmarked straightedge and a compass.. Pierre Wantzel proved in 1837 that the problem, as stated, is impossible to solve for arbitrary angles.