Question

In an ellipse the distance between the foci is 8 and the distance between the directrices is 25. The length of the major axis is-

• A. 10$\sqrt{2}$
• B. 20$\sqrt{2}$
• C. 30$\sqrt{2}$
• D. None of these

Answer 1

Answer: (A)

10$\sqrt{2}$

Answer 2

2ae = 8 Ž ae=4Ža=4/e, 2a/e=25 \2(4/e)/e = 25

Ž8/e²=25,e²=8/25Že=$2\sqrt{2}/5$\a=$4/2\sqrt{2}/5$=$20/2\sqrt{2}$=$10/\sqrt{2}$=5$\sqrt{2}$\l. of major axis

=2a= 10$\sqrt{2}$