Parabola 3Given the axis, the axial vertex (V), and one point (P) on the curve, construct the parabola.  From the given point P construct line PA perpendicular to the axis and intersecting it at A. Construct B on the axis such that V is the midpoint of AB. Line PB is tangent to the curve. Construct a diameter through P parallel to the axis. Reflect the diameter across PB. The reflected line intersects the axis at focus F. Reflect F across PB to image point Fʹ, which lies on the directrix. Construct the directrix through Fʹ, perpendicular to the axis.  Now the parabola construction is completed from the focus and directrix. Drag the given objects on the image below to confirm the construction. |