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 Rn1,n>1  

Rn: rectangle of largest area, with sides parallel to the axes, inscribed in  En,n>1

Then which of the following options is/are correct?

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a

The length of latus rectum of E9 is 16

b

The eccentricities of E18 and E19are NOT equal

c

n=1Narea   of   Rn<24 for each integer 

d

The distance of a focus from the center E9 is 532

answer is B, C.

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Detailed Solution

E1:x29+y24=1( ellipse ),e=53R1: Max. Rectangle inscribed having sides parallel to axes 

 For this A=(3cosθ,2sinθ), where θ=π4 i.e A=32,32 Sides: 32,22 Area of R1=(32)(22) If a.b are semi axes of ellipse then a2,b2 are sides. 

 For E2:x2322+y2222=1 i.e. semi axes are a2,b2 . E9:x23(2)82+y22(2)82 distance from centre to foucs of E9=ae

3(2)8×53=516   L.L. R=2b2a=2×2(2)823(2)8=2×4256316=132×163=16

 Eccentricities for all ellipses are equal.  Also sum of areas =R1+R2+R3 =4 Areas sum in Q1=43222+3(2)22(2)2+3(2)3223+=4612+14+18+.=24×121-12=24n=1N area of Rn<24

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