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Question

For all complex numbers z1,z2satisfying|z1|=12,|z234i|=5, the minimum value of |z1z2| is


A
0
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B
7
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C
2
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D
17
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Solution

The correct option is C 2
We have, |z1|=12. Therefore z1 lies on the circle with centre (0,0) and radius 12 units and |z234i| is a circle with centre (3,4) and radius 5 units.



From above figure it is clear that |z1z2|, i.e. distance between z1 and z2 will be minimum when they lie at 𝐴 and 𝐵 respectively.
Then, |z1z2|=AB=OAOB=122×5=2



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