Through the vertex `' O^(prime)` of the parabola `y^2=4a x ,` variable chords `O Pa n dO Q` are drawn at right angles. If the variable chord `P Q` intersects the axis of `x` at `R` , then distance `O R :` equals double the perpendicular distance of focus from the directrix. equal the semi latus rectum of the parabola equals latus rectum of the parabola equals double the latus rectum of the parabola