4-1.Complex numbers
easy

यदि सम्मिश्र संख्याओं ${z_1}$ तथा  ${z_2}$ के लिये $arg({z_1}/{z_2}) = 0,$तब $|{z_1} - {z_2}|$ =

A

$|{z_1}| + |{z_2}|$

B

$|{z_1}| - |{z_2}|$

C

$||{z_1}| - |{z_2}||$

D

$0$

Solution

(c) हम जानते हैं कि $|{z_1} – {z_2}{|^2}$

$ = |{z_1}{|^2} + |{z_2}{|^2} – 2|{z_1}||{z_2}|\cos ({\theta _1} – {\theta _2})$

जहाँ ${\theta _1} = arg({z_1})$ एवं ${\theta _2} = arg({z_2})$

$arg\,{z_1} – arg\,{z_2} = 0$

$|{z_1} – {z_2}{|^2} = |{z_1}{|^2} + |{z_2}{|^2} – 2|{z_1}||{z_2}| = {(|{z_1}| – |{z_2}|)^2}$

$⇒ |{z_1} – {z_2}| = ||{z_1}| – |{z_2}||$

Standard 11
Mathematics

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