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Q.

Three circles, each of radius 1, are packed inside an ellipse x2a2+y2b2=1(a>b>0),  (2θ=ABC),
 as shown in the fig. Two of these circles, touch the ellipse at two points each, and the middle circle touches it at the end of minor axis. A, B and C are centres of these circles. 
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If the area of ellipse is minimum, then which of the following options is/are correct?  
 

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a

6tanθ=35

b

6e=5

c

3b = 4

d

a=43

answer is B, C.

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Detailed Solution

E:  x2a2+y2b2=1

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area,  Δ=π  ab    OBJ:  Δ=f(θ)      b2  cosθ=1  b=1+2cosθ

Also normal to ellipse at H passes through C 

Let  H(p,  q)N@Ha2xpb2yq=a2b2=a2e2c(pe2,  0)

pe2=2sinθ  and   b1=2cosθ    (pe2)2+(b1)2=4

HC=1  (p2sinθ)2+q2=1

HC=1  (p2sinθ)2+q2=1   (p(1e2))2+q2=1

also  H  lies  on  ellipse  p2a2+q2b2=1p2(1e2)+q2=b2

p2e2(1e2)=b21  and  p2e4=4(b1)2

1e2e2=b213b2+2b1e2=b212+2b=b2a2

a2=2b2b1Δ=πab=πb22b1=π2b3b4

dΔdb=0b=432cosθ=13tanθ=35

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