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Question

Let z1 and z2 be two complex numbers such that |z1|=12 and |z234i|=5. Then the minimum value of |z1z2| is

A
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B
2
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C
7
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D
17
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Solution

The correct option is B 2
Given, |z1|=12 and |z234i|=5
|z1z2|=|z1(z234i)(3+4i)|
Using the inequality,
|z1z2||z1||z2| for any two complex numbers z1 and z2, we get
|z1(z234i)(3+4i)|||z1||z234i||3+4i||
|z1z2||1255|
|z1z2|2
Hence, the minimum value of |z1z2| is 2.

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