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← JEE Main 2022 · 24 Jun · Shift 1
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JEE Main 2022 · 24 Jun · Shift 1, Mathematics question 1

Let A={z∈C:1≤∣z−(1+i)∣≤2}A=\{z\in\mathbb C:1\le|z-(1+i)|\le2\} and B={z∈A:∣z−(1−i)∣=1}B=\{z\in A:|z-(1-i)|=1\}. Then, BB :

Choose one option
Answer and worked solution

Official answer: D

Picture it. AA is the closed annulus about 1+i1+i with radii 1 and 2. BB is the part of the circle ∣z−(1−i)∣=1|z-(1-i)|=1 (centre 1−i1-i, radius 1) lying in AA.

Distances. The centres are 2 apart, so points of the circle are at distance between 2−1=12-1=1 and 2+1=32+1=3 from 1+i1+i. The points with distance in [1,2][1,2] form a whole arc (from the nearest point, at distance 1, out to where the distance reaches 2).

Conclusion. An arc has infinitely many points.

(D)