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10-2. Parabola, Ellipse, Hyperbola
normal
In an ellipse, the distance between its foci is $6$ and minor axis is $8.$ Then its eccentricity is :
A
$\frac{3}{5}$
B
$\frac{1}{2}$
C
$\frac{4}{5}$
D
$\frac{1}{\sqrt 5}$
Solution
$2 \mathrm{ae}=6 \Rightarrow \mathrm{ae}=3$
Minor axis $=2 b=8 \Rightarrow b=4$
As, $b^{2}=a^{2}\left(1-e^{2}\right) \Rightarrow 16=a^{2}-a^{2} e^{2}$
$\Rightarrow 16=a^{2}-9$
$\Rightarrow \mathrm{a}^{2}=25 \Rightarrow \mathrm{a}=5$
ae $=3 \Rightarrow \mathrm{e}=\frac{3}{5}$
Standard 11
Mathematics