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MathematicsComplex NumberGeometric ApplicationHard2 minPYQ_2021
MathematicsHardsingle choice

Let the lines2-iz=2+iz¯and2+iz+i-2z¯-4i=0,(herei2=-1) be normal to a circleC. If the lineiz+z¯+1+i=0is tangent to this circleC, then its radius is :

Options:

Answer:
C
Solution:

(2-i)z=(2+i)z¯

(2-i)(x+iy)=(2+i)(x-iy)

2x-ix+2iy+y=2x+ix-2iy+y

2ix-4iy=0

L1:x-2y=0

(2+i)z+(i-2)z¯-4i=0

(2+i)(x+iy)+(i-2)(x-iy)-4i=0

.2x+ix+2iy-y+ix-2x+y+2iy-4i=0

2ix+4iy-4i=0

Solve L1 and L2, 4y=2, y=12

 x=1

Centre 1,12

L3:iz+z¯+1+i=0

i(x+iy)+x-iy+1+i=0

ix-y+x-iy+1+i=0

(x-y+1)+i(x-y+1)=0

Radius = distance from 1, 12 to x-y+1=0

r=1-12+12

r=322

Stream:JEESubject:MathematicsTopic:Complex NumberSubtopic:Geometric Application
2mℹ️ Source: PYQ_2021

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