Q53 of 63 Page 202

If the vertex of the parabola is the point (–3, 0) and the directrix is the line x + 5 = 0, then its equation is

Vertex = (-3, 0) & Directrix is x + 5 = 0 (Intersection point is (-5, 0)


As , the co-ordinates of focus is the mid – point of the co-ordinates of vertex & the point of intersection of directrix and x or y axis respectively.


Focus = (p,q)




p = -1 & q = 0


Focus is (-1, 0)


For any point on parabola, P(x,y) the distance of focus from that point is always equal to the perpendicular distance from that point to the directrix.


Perpendicular Distance (Between a point and line) = , whereas the point is and the line is expressed as ax + by + c = 0 x + 5 = 0


Using Distance Formula,





Squaring both the sides,



x2 + 2x + 1 + y2 = x2 + 25 + 10x


y2 = 8x + 24


y2 = 8 (x + 3)


Hence the required equation is y2 = 8 (x + 3).


OPTION (A) is the correct answer.

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