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If α and β are different complex numbers with |β| = 1, then find |β-α1-α¯β|

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Question

If α and β are different complex numbers with |β| = 1, then find `|(beta - alpha)/(1-baralphabeta)|`

Sum
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Solution

`|(beta - alpha)/(1 - baralpha beta)|^2`

= `((beta - alpha)/(1 - baralpha beta))bar(((beta - alpha)/(1 - baralpha beta))`

= `(beta - alpha)/(1 - baralpha beta) xx (barbeta - baralpha)/(1 - baralpha beta)`

= `(beta barbeta - baralphabeta - alpha barbeta + alpha baralpha)/(1 - alpha barbeta - baralphabeta +alphabaralpha.betabarbeta)`

= `(|beta|^2 - baralphabeta  - alphabarbeta + |alpha|^2)/(1 - alphabarbeta  -  baralphabeta  + |alpha|^2 . |beta|^2`)`

Given |β| = 1,

= `(1 + |alpha|^2 - baralphabeta  -  alphabarbeta)/(1 + |alpha|^2 - baralphabeta - alphabarbeta)`

= 1

∴ `|(beta - alpha)/(1 - baralphabeta)|  =  1` or `|(beta - alpha)/(1 - baralphabeta)|  = 1`

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Chapter 4: Complex Numbers and Quadratic Equations - Miscellaneous Exercise [Page 86]

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NCERT Mathematics [English] Class 11
Chapter 4 Complex Numbers and Quadratic Equations
Miscellaneous Exercise | Q 11. | Page 86

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