Q.

Define the collections {E1, E2, E3,……} of ellipses and {R1, R2, R3,…..} of rectangles as follows:E1:x29+y24=1;

R1: Rectangle of largest area, with sides parallel to the axes, inscribed in E1; En: Ellipse x2an2+y2bn2=1 of largest area inscribed in Rn-1,n>1 ; Rn: Rectangle of largest area, with sides parallel to the axes, inscribed in En, n>1. Then which of the following option(s) is/are correct?

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a

n=1Narea of Rn<24,for each positive integer N

b

 The distance of a focus from the centre in E8 is 532

c

The eccentricities of E2019­ and E2020 are equal

d

 The length of latus rectum of E9 is 16

answer is A, C, D.

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Detailed Solution

Question Image

 Area of R1=3sin2θ ; for this to be maximum 

θ=π432,22

Hence for subsequent areas of rectangles Rn

 to be maximum the coordinates will be in GP with common ratio 

r=12an=32n1;bn=32n1

Eccentricity of all the ellipses will be same

          Distance of a focus from the centre inE9=a9e9=a92b92=516

 Length of latus rectum of E9=2 b92a9=16

n=1Area  of  Rn=12+122+124+..........=24

n=1Area  of  Rn<24for each positive integer N

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Define the collections {E1, E2, E3,……} of ellipses and {R1, R2, R3,…..} of rectangles as follows:E1:x29+y24=1;R1: Rectangle of largest area, with sides parallel to the axes, inscribed in E1; En: Ellipse x2an2+y2bn2=1 of largest area inscribed in Rn-1,n>1 ; Rn: Rectangle of largest area, with sides parallel to the axes, inscribed in En, n>1. Then which of the following option(s) is/are correct?