Parabola 1 Question 10

10. If the line x1=0 is the directrix of the parabola y2kx+8=0, then one of the values of k is

(a) 18

(b) 8

(c) 4

(d) 14

(2000, 2M)

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Answer:

Correct Answer: 10. (c)

Solution:

  1. Given,

y2=kx8

y2=kx8k

Shifting the origin Y2=kX, where Y=y,X=x8/k.

Directrix of standard parabola is X=k4 Directrix of original parabola is x=8kk4

Now, x=1 also coincides with x=8kk4

On solving, we get k=4



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