Let S1,S2,S3 be S1={z∈C:∣z−1∣≤2}, S2={z∈C:Re[(1−i)z]≥1}, S3={z∈C:Im(z)≤1}. Then the set S1∩S2∩S3
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Official solution
S1 is a disk of radius 2 about (1,0); S2 is the half-plane x+y≥1; S3 is the half-plane y≤1. Sketching these three regions shows they overlap in a two-dimensional region, so S1∩S2∩S3 has infinitely many elements.