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If the line x-1=0 is the directrix of th...

If the line `x-1=0` is the directrix of the parabola `y^2-k x+8=0` , then one of the values of `k` is (a)`1/8` (b) 8 (c) 4 (d) `1/4`

A

-8

B

`1//8`

C

`1//4`

D

4

Text Solution

Verified by Experts

1,4
We have equation of parabola,
`y^(2)=kx-8ory^(2)=k(x-(8)/(k))`
Equation of directrix is
`x-(8)/(k)=-(k)/(4)orx=-(k)/(4)+(8)/(k)`
Given equation of directrix is x=1.
`:.(8)/(k)-(k)/(4)=1`
`rArrk^(2)+4k-32=0`

`rArr(k-4)(k+8)=0`
`rArrk=-8,4`
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