Complex Numbers 2 Question 12

12. If w=α+iβ, where β0 and z1, satisfies the condition that ww¯z1z is purely real, then the set of values of z is

(2006,3M)

(a) |z|=1,z2

(b) |z|=1 and z1

(c) z=z¯

(d) None of these

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Answer:

Correct Answer: 12. (a)

Solution:

  1. Let z1=ww¯z1z be purely real z1=z¯1

1zww¯z1z=w¯wz¯1z¯

wwz¯w¯z+w¯zz¯=w¯zw¯wz¯+wzz¯

(ww¯)+(w¯w)|z|2=0

(ww¯)(1|z|2)=0

|z|2=1 [as ww¯0, since β0]

|z|=1 and z1



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