Q. 35.0( 1 Vote )

Write the equation of the directrix of the parabola x2 – 4x – 8y + 12 = 0

Answer :

Given equation of the parabola is x2 - 4x - 8y + 12 = 0



x2 - 4x + 12 = 8y


x2 - 4x + 4 = 8y - 8


(x - 2)2 = 8(y - 1)


Comparing with the standard form of parabola (x - a)2 = 4b(y - c) we get,


4b = 8


b = 2


The equation of the directrix is y - c = - b


Directrix is y - 1 = - 2


Directrix is y = - 2 + 1


Directrix is y = - 1


The equation of the directrix is y = - 1.


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