# Conchoids

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)

*P*and*P'*is called a**conchoid****.***of S with respect to A*## The Conchoid of Nicomedes

## Other Conchoids

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.