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For an ellipse, the distance between the two foci is 10 and the distance between a focus and its corresponding directrix is 15. If the eccentricity is e, find the value of 4e.
- 2
- 3
- 1
- 8/3
Correct answer: 2
Solution
From 2ae = 10 and a/e - ae = 15, solving gives e = 1/2, so 4e = 2.
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