Question 980712
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Mathematics sort of cheats on this one, and defines the directrix of a circle as "the line at infinity", meaning the line is an infinite distance from the circle. Dividing a fixed number (focus to circle, or radius) by infinity is "approaching zero". Draw your imaginary directrix an imagined infinity from your circle, and while the ratio e becomes zero for practical purposes, it raises more questions for math theorists to ponder, and may raise questions from you that can be answered more clearly.