Let an ellipse E : x 2 a 2 + y 2   b 2 = 1 , a 2 > b 2 , passes through 3 2 , 1 and has…

Let an ellipse E:x2a2+y2 b2=1,a2>b2, passes through 32,1 and has eccentricity 13. If a circle, centered at focus F(α,0),α>0, of E and radius 23, intersects E at two points P and Q, then PQ2 is equal to :
  1. 83
  2. 43
  3. 163
  4. 3

Solution

The ellipse x2a2+y2b2=1 passes through the point 32,1

So, 32a2+1b2=1   ...1 and 1-b2a2=13   ...2

On solving equations 1 and 2, we get

a2=3 & b2=2

x23+y22=1   ...3

We know that, focii of the ellipse x2a2+y2b2=1 is ±ae, 0

Here, a=3 & e=13

 Its focus is 1,0 α>0

Now, equation of circle is

(x-1)2+y2=43   ...4

Solving 3 and 4 we get

y=±23,x=1

PQ2=1-12+23+232

=432=163

Asked in: JEE Main 2021 (25 Jul Shift 1)

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