(generalized) strophoid


last updated: 2003-08-01

Given a curve C1 and fixed points O (pole) and A (another point). Draw lines l through O that intersect C1 in Q. Then the strophoid is defined as the collection of points P (on l) for which PQ is equal to a AQ.

Some special cases:

curve C1 pole O fixed point A strophoid
line not on C1 on C1 oblique strophoid
line not on C1 projection of O on C1
(right) strophoid
circle center of C1 on C1 Freeth's nephroid
trisectrix of Maclaurin ... ... Freeth's strophoid