Question:

Let \(z_1\) and \(z_2\) be two complex numbers satisfying \(|z_1|=9\) and \(|z_2-3-4i|=4\). Then the minimum value of \(|z_1-z_2|\) is :

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Both circles are in the plane: one centred at the origin with radius 9, other centred at 3+4i with radius 4; compare the distance between centres with the radii.
Updated On: Nov 5, 2026
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  • \(\sqrt2\)
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The Correct Option is A

Solution and Explanation

\(z_1\) lies on the circle \(C_1\): centre 0, radius 9. \(z_2\) lies on \(C_2\): centre \(3+4i\), radius 4.
Distance between centres \(=|3+4i|=5\). Since \(5+4=9\), \(C_2\) lies inside \(C_1\) and touches it internally at one point.
At the point of contact \(z_1=z_2\), so the minimum of \(|z_1-z_2|\) is 0.
Answer: (1) 0
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