Question

If the distance from the focus is 3 units and the distance from the directrix is 3 units, then how much is the eccentricity?

(a) Infinity

(b) Zero

(c) Unity

(d) Less than one

This question was posed to me during an online exam.

Origin of the question is Basics of Conic Sections in division Curves used in Engineering Practice of Engineering Drawing

Answer 1

Correct answer is (c) Unity

The explanation is: Eccentricity is defined as the ration of the distance from the focus to the distance from the directrix and it is denoted as e. Hence from the definition, e = 3 ÷ 3 = 1. Hence the value of eccentricity is equal to unity.