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If the line x - 1 = 0 is the directrix of the parabola y² - k*x + 8 = 0, then one possible value of k is:
- 1/8
- 8
- 4
- 1/4
Correct answer: 4
Solution
y² = k(x - 8/k) gives vertex x = 8/k and a = k/4; directrix x = 8/k - k/4 = 1 yields k = 4.
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