- Steve Phelps
Let S be any curve and let A be a fixed point. If a straight line is drawn through A to meet S at Q, and if P and P' are points on this line such that
P'Q = QP = k (a constant)the locus of P and P' is called a conchoid of S with respect to A.
The Conchoid of Nicomedes
The conchoid of a circle of radius r with respect to a point within it.
A conchoid of a parabola with respect to the focus
A conchoid of an ellipse or hyperbola with respect to a focus.