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10-2. Parabola, Ellipse, Hyperbola
easy
In the ellipse, minor axis is $8$ and eccentricity is $\frac{{\sqrt 5 }}{3}$. Then major axis is
A
$6$
B
$12$
C
$10$
D
$16$
Solution
(b) Given, minor axis of ellipse $e = 1/\sqrt 2 $ or $b = 4$ and eccentricity $(e) = \sqrt 5 /3$.
We know that in an ellipse, ${e^2} = 1 – \frac{{{b^2}}}{{{a^2}}}$ or $\frac{5}{9} = 1 – \frac{{16}}{{{a^2}}}$
or $\frac{{16}}{{{a^2}}} = 1 – \frac{5}{9}$ or ${a^2} = \frac{{16 \times 9}}{4}$$ = 36$ or $a = 6.$
We also know that major axis of the ellipse $ = 2a = 2 \times 6 = 12.$
Standard 11
Mathematics