Secant line a circle in the Euclidean plane, a line joining two of them would be a 2-secant (or "bisecant") and a line passing through only one of them would be a 1-secant (or "unisecant"). A unisecant in this example need not be a tangent line to the circle. This terminology is often used in incidence geometry and discrete geometry. For instance, the Sylvester–Gallai theorem of incidence geometry states that if points of Euclidean geometry are not collinear then there must exist a 2-secant of them. And the original orchard-planting problem of discrete geometry asks for a bound on the number of
Polar circle (geometry) Polar circle (geometry) In geometry, the polar circle of a triangle is the circle whose center is the triangle's orthocenter and whose squared radius is where "A, B, C" denote both the triangle's vertices and the angle measures at those vertices, "H" is the orthocenter (the intersection of the triangle's altitudes), "D", "E", "F" are the feet of the altitudes from vertices "A, B, C" respectively, "R" is the triangle's circumradius (the radius of its circumscribed circle), and "a", "b", "c" are the lengths of the triangle's sides opposite vertices "A", "B", "C" respectively. The first parts of the radius