Conic Construction

The one conic construction that is probably what you know if you know one is the parabola construction. <\br> <\br> In the construction above, the line through A and B is the directrix. Point C is the focus. Point D is placed on line AB and is free to move along the line. A line perpendicular to lina AB is erected at point D. A perpendicular bisector of the points C and D is constructed. The point E where this perpendicular bisector intersects the perperndicular to line AB at point D is equally distant from point C and the line AB, meaning it lies on the parabola with the directrix line AB and the focus C.