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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

Options

  1. A1 8
  2. B8
  3. C1 4
  4. D4

Correct answer

D. 4

Step-by-step solution

Given, y 2 = k x - 8   ⇒ y 2 = k x - 8 k Shifting the origin Y 2 = k X where Y = y ,   X = x - 8 k Directrix of standard parabola is X = - k 4 Directrix of original parabola is x = 8 k - k 4 Now, x = 1 also coincides with x = 8 k - k 4 On solving, we get k = 4 , - 8

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