UPSC NDA Math Model Paper 3

Here, we have to find the eccentricity of the ellipse whose length of major axis is 20 units and its foci are (±5√3,0) .
As we know that, for a horizontal ellipse i.e

x2

a2

+

y2

b2

=1 we have foci at (± ae, 0) and length of major axis is given by 2a.
⇒ 2a = 20 and ae = 5√3
So, a = 10
⇒e=(5√3)∕10=√3∕2
Hence, option C is the correct answer.