Complex Numbers 2 Question 14

14. For all complex numbers z1,z2 satisfying |z1|=12 and |z234i|=5, the minimum value of |z1z2| is

(a) 0

(b) 2

(c) 7

(d) 17

(2002, 1M)

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Answer:

Correct Answer: 14. (a)

Solution:

  1. We know, |z1z2|=|z1(z234i)(3+4i)|

|z1||z234i||3+4i|1255 [using |z1z2||z1||z2|]

|z1z2|2

Alternate Solution

Clearly from the figure |z1z2| is minimum when z1,z2 lie along the diameter.

|z1z2|C2BC2A1210=2



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