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Question: Answered & Verified by Expert

Let w=zz¯+k1z+k2iz+λ(1+i),k1,k2. . Let Re(w)=0 be the circle C of radius 1 in the first quadrant touching the line y=1 and the y-axis. If the curve Im(w)=0 intersects C at A and B, then 30(AB)2 is equal to _______.

MathematicsComplex NumberJEE MainJEE Main 2023 (13 Apr Shift 1)
Solution:
2036 Upvotes Verified Answer
The correct answer is: 24

Given,

w=zz¯+k1z+k2iz+λ(1+i),k1,k2. .

And Re(w)=0,

So, taking z=x+iy & z¯=x-iy

We get,

w=x2+y2+k1x+iy+k2ix+iy+λ(1+i)

Rew=0x2+y2+k1x-k2y+λ=0

And, Im(w)=0k1y+k2x+λ=0

Now given Re(w)=0 circle is touching y=1 and y-axis, with radius 1, so we have equation of circle

x2+y2-2x-4y+4=0

So, on comparing with Re(w)=0 we get,

k1=-2,k2=4,λ=4

So, Im(w)=0-2y+4x+4=0

And given -2 y+4 x+4=0 intersects the circle,

So, solving x2+y2-2x-4y+4=0 and -2 y+4 x+4=0 we get,

Intersecting point as A0,2 and B25,145

Hence, by distance formula we get,

30(AB)2=300-252+2-1452=24

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