Strophoid

In geometry, a strophoid is a curve generated from a given curve C and points A (the fixed point) and O (the pole) as follows: Let L be a variable line passing through O and intersecting C at K. Now let P₁ and P₂ be the two points on L whose distance from K is the same as the distance from A to K. The locus of such points P₁ and P₂ is then the strophoid of C with respect to the pole O and fixed point A. Note that AP₁ and AP₂ are at right angles in this construction.