The pedal curve of the parabolawith parametric equations(1)(2)with pedal point is(3)(4)On the conic section directrix, the pedal curve of a parabola is a strophoid (top left). On the foot of the conic section directrix, it is a right strophoid (top middle). On reflection of the focus in the conic section directrix, it is a Maclaurin trisectrix (top right). On the parabola vertex, it is a cissoid of Diocles (bottom left; Gray 1997, p. 119). On the focus, it is a straight line (bottom right; Hilbert and Cohn-Vossen 1999, pp. 26-27). On the symmetry axis for a parabola with , it is a conchoid of de Sluze (H. Smith, pers. comm., Aug. 4, 2004). The following table summarizes these special cases.pedal pointpedal curvedirectrixstrophoidfoot of directrixright strophoidreflection of focus in directrixMaclaurin trisectrixparabola vertexcissoid of Dioclesfocuslineaxis of a parabola with conchoid of de Sluze..
A wheel graph of order , sometimes simply called an -wheel (Harary 1994, p. 46; Pemmaraju and Skiena 2003, p. 248; Tutte 2005, p. 78), is a graph that contains a cycle of order , and for which every graph vertex in the cycle is connected to one other graph vertex (which is known as the hub). The edges of a wheel which include the hub are called spokes (Skiena 1990, p. 146). The wheel can be defined as the graph , where is the singleton graph and is the cycle graph. Note that there are two conventions for the indexing for wheel graphs, with some authors (e.g., Gallian 2007), adopting the convention that denotes the wheel graph on nodes.The tetrahedral graph (i.e., ) is isomorphic to , and is isomorphic to the complete tripartite graph . In general, the -wheel graph is the skeleton of an -pyramid. is one of the two graphs obtained by removing two edges from the pentatope graph , the other being the house X graph.Wheel graphs are graceful (Frucht..