Question

The eccentricity of an ellipse in which distance between their focii is 10 and that of focus and corresponding directrix is 15 is

• A. $\frac{1}{3}$
• B. $\frac{1}{2}$
• C. $\frac{1}{4}$
• D. $\frac{1}{\sqrt{2}}$

Answer 1

Answer: (B)

$2 a e=10 \,\, \frac{a}{e}-a e=15$
$a e=5 \,\, \frac{5}{e^2}-5=15 \Rightarrow \frac{5}{e^2}=20 \Rightarrow e=\frac{1}{2}$