Let mathbbC be the set of all complex numbers. Let S_1=z∈ mathbbC:|z-2|≤ 1 and S_2=z∈ mathbbC:z(1+i)+ z(1-i)≥ 4. Then, the maximum value of |z- 5…
JEE Main 2021 — Mathematics Algebra
2021mcqhard
Let C be the set of all complex numbers. Let S1=z∈C:∣z−2∣≤1 and S2=z∈C:z(1+i)+zˉ(1−i)≥4. Then, the maximum value of ∣z−25∣2 for z∈S1∩S2 is equal to :
Official previous-year question
Held on 27 Jul 2021 · Verified 6 Jul 2026.
Options
A
43+22
B
25+22
C
23+22
D
45+22
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Solution
Here, ∣z−2∣≤1 Put z=x+iy
(x−2)2+y2≤1
Also, z(1+i)+zˉ(1−i)≥4
Gives x−y≥2
Let point on circle be A(2+cosθ,sinθ)
θ∈[−43π,4π]
Let P be (25,0)
So,
∣z−25∣2=(AP)2=(2+cosθ−25)2+sin2θ
=cos2θ−cosθ+41+sin2θ
=45−cosθ
For (AP)2 to be maximum θ=−43π
(AP)2=45+21=4252+4=45+22
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