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QJEEM22Mae39f: JEE Main 2022 Mathematics - Class 11 JEEM22Mae39f Solution: Let be complex numbers satisfying . Then the least value of ,…

Let z=a+ib,b≠0\mathrm{z}=a+i b, b \neq 0 be complex numbers satisfying z2=zˉ⋅21−zz^{2}=\bar{z} \cdot 2^{1-z} . Then the least value of n∈Nn \in N , such that zn=(z+1)nz^{n}=(z+1)^{n} , is equal to __________.

Step-by-Step Verified Solution

∵\because z2=z‾ . 21−∣z∣{z^2} = \overline z \,.\,{2^{1 - |z|}} ...... (1)

⇒∣z∣2=∣z‾∣ . 21−∣z∣\Rightarrow |z{|^2} = |\overline z |\,.\,{2^{1 - |z|}}

⇒∣z∣=21−∣z∣\Rightarrow |z| = {2^{1 - |z|}} ,

∵\because b≠0⇒∣z∣≠0b \ne 0 \Rightarrow |z| \ne 0

∴\therefore ∣z∣=1|z| = 1 ...... (2)

∵\because z=a+ibz = a + ib then a2+b2=1\sqrt {{a^2} + {b^2}} = 1 ...... (3)

Now again from equation (1), equation (2), equation (3) we get :

a2−b2+i2ab=(a−ib)20{a^2} - {b^2} + i2ab = (a - ib){2^0}

∴\therefore a2−b2=a{a^2} - {b^2} = a and 2ab=−b2ab = - b

∴\therefore a=−12a = - {1 \over 2} and b= ± 32b = \, \pm \,{{\sqrt 3 } \over 2}

z=−12+32iz = - {1 \over 2} + {{\sqrt 3 } \over 2}i or z=−12−32iz = - {1 \over 2} - {{\sqrt 3 } \over 2}i

zn=(z+1)n⇒(z+1z)n=1{z^n} = {(z + 1)^n} \Rightarrow {\left( {{{z + 1} \over z}} \right)^n} = 1

(1+1z)n=1{\left( {1 + {1 \over z}} \right)^n} = 1

(1+3i2)=1\left( {{{1 + \sqrt 3 i} \over 2}} \right) = 1 , then minimum value of n is 6.

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