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Where does z lie, if |z-5iz+5i| = 1.

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Question

Where does z lie, if `|(z - 5i)/(z + 5i)|` = 1.

Sum
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Solution

Given that: `|(z - 5i)/(z + 5i)|` = 1

Let z = x + yi

∴ `|(x + yi - 5i)/(x + yi + 5i)|` = 1

⇒ `|(x + (y - 5)i)/(x + (y + 5)i)|` = 1

⇒ `|x + (y - 5)i| = |x + (y + 5)i|`

⇒ `x^2 + (y - 5)^2 = x^2 + (y + 5)^2`

⇒ `(y - 5)^2 = (y + 5)^2`

⇒ y2 + 25 – 10y = y2 + 25 + 10y

⇒ 20y = 0

⇒ y = 0

Hence, z lies on x-axis i.e., real axis.

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Chapter 5: Complex Numbers and Quadratic Equations - Exercise [Page 95]

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NCERT Exemplar Mathematics Exemplar [English] Class 11
Chapter 5 Complex Numbers and Quadratic Equations
Exercise | Q 34 | Page 95

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