Gujarati
10-2. Parabola, Ellipse, Hyperbola
easy

The distance between the directrices of a rectangular hyperbola is $10$ units, then distance between its foci is

A

$10\sqrt 2 $

B

$5$

C

$5\sqrt 2 $

D

$20$

Solution

(d) Distance between directrices $ = \frac{{2a}}{e}$.

Eccentricity of rectangular hyperbola $ = \sqrt 2 $.

 Distance between directrics $ = \frac{{2a}}{{\sqrt 2 }}$.

Given that , $\frac{{2a}}{{\sqrt 2 }} = 10$

==> $2a = 10\sqrt 2 $

Now, distance between foci $ = 2ae = (10\sqrt 2 )\,(\sqrt 2 ) = 20.$

Standard 11
Mathematics

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