Among the statements (S1) : The set \z C - \-i\ : |z| = 1 and z - iz + i is purely real \ contains exactly two elements, and (S2) : The set \z C - \-1\ : |z| = 1 and z - 1z + 1 is purely imaginary \ contains infinitely many elements.
- both are incorrect
- both are correct
- only (S2) is correct
- only (S1) is correct
Answer
(3) only (S2) is correct
Solution
(S1): z - iz + i is real z, i and −i are collinear z lies on the imaginary axis.
With |z| = 1: z = i or z = -i; but z -i.
the set is \i\ (one element only). (S1) is incorrect.
(S2): Let z = + i , .
z - 1z + 1 = ei - 1ei + 1 = ei /2 - e-i /2ei /2 + e-i /2 = i 2
purely imaginary for every (- , ), 0 — infinitely many z. (S2) is correct.
Answer: (3)