The smallest positive integer n for which \(\left(\frac{1+i}{1 - i}\right)^n = 1\), is

  1. 1
  2. 2
  3. 3
  4. 4

Answer (Detailed Solution Below)

Option 4 : 4
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Detailed Solution

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Concept:

  • The complex unit i is defined as \(\rm i=\sqrt{-1}\).
  • i2 = -1, i3 = - i, i4 = 1 etc.
  • (a + b)2 = a2 + 2ab + b2

 

Calculation:

Given that,

\(\left(\frac{1+i}{1 - i}\right)^n = 1\)    ---(1)

Let, y = \(\left(\frac{1+i}{1 - i}\right)\)

\(\Rightarrow \ y=\dfrac{1+i}{1-i}\times \dfrac{1+i}{1+i}\).

\(\Rightarrow\ y\ =\dfrac{(1+i)^2}{1^2-i^2}\)

∵ (a + b)2 = a2 + 2ab + b2

\(\Rightarrow\ y\ =\dfrac{1+2i+i^2}{1-i^2}\)

\(\Rightarrow y\ =\dfrac{2i}{2}=i\)    (∵ i2 = -1)

Therefore, from equation (1)

\( \left(\dfrac{1+i}{1-i}\right)^n=\ i^n\ =\ 1\)

The smallest positive integer for which in = 1 is n = 4.

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