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Question

If xāˆ’1=0 is the directix of parabola y2āˆ’kx+8=0, then k is equal to

A
1/8
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B
8
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C
4
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D
1/4
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Solution

The correct option is A 4
We have, y2kx8=0
y2=k(x8k)
Directrix x8k=k4
x(8kk4)=0
But equation of directrix is x1=0. Hence, by comparing, we get
8kk4=1k2+4k32=0
(k4)(k+8)=0
k=4,8.

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