At any point on the curve 2x2y2−x4=c, the mean proportional between the abscissa and the difference between the abscissa and the sub-normal drawn to the curve at the same point is equal to
(a) ordinate
(b) radius vector
(c) x-intercept of tangent
(d) sub-tangent
(a) ordinate
(b) radius vector
(c) x-intercept of tangent
(d) sub-tangent