Gujarati
Hindi
10-2. Parabola, Ellipse, Hyperbola
normal

The eccentricity of an ellipse whose length of latus rectum is equal to distance between its foci, is

A

$2\,sin\,18^o$

B

$2\,cos\,36^o$

C

$sin\,18^o$

D

$cos\,36^o$

Solution

$\frac{2 b^{2}}{a}=2 a e $

$\Rightarrow a^{2}\left(1-e^{2}\right)=a^{2} e$

$\Rightarrow e^{2}+e-1=0 $

$\Rightarrow e=\frac{\sqrt{5}-1}{2}$

$=2 \sin 18^{\circ}$

Standard 11
Mathematics

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