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If (1+i1-i)m = 1, then find the least positive integral value of m.

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Question

If `((1+i)/(1-i))^m` = 1, then find the least positive integral value of m.

Sum
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Solution

`((1+i)/(1-i))^m` =   1, 

⇒ `((1+i)/(1-i) xx (1 + i)/(1 + i))^m` =   1, 

⇒ `((1+ i)^2/(1^2 + 1^2))^m  = 1`

⇒ `((1^2  + i^2  + 2i)/2)^2  = 1`

⇒ `((1 - 1 + 2i)/2)^2 = 1`

⇒ `((2i)/2)^m  = 1`

⇒ `i^m  = 1`

∴ m = 4k, where k is an integral

Therefore, the smallest positive integral is 1

Therefore, the least positive integral value of m is 4 (4 x 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 14. | Page 86

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