If a focal chord of the parabola y2=ax is 2x−y−8=0, then the equation of the directrix is
A
y+4=0
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B
x−4=0
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C
y−4=0
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D
x+4=0
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Solution
The correct option is Dx+4=0 Since, focal chord of parabola y2=ax is 2x−y−8=0. Also, this chord passes through focus (a4,0) ∴2a4−0−8=0⇒a=16 ∴ Directrix is x=−4⇒x+4=0