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JEE Main 202228 JulyEvening Shift
Exam
JEE Main
Year
2022
Date
28 July
Shift
Evening Shift
Subject
Mathematics
Chapter
Complex Number

JEE Main 2022 · 28 July · Evening Shift · Mathematics · Complex Number

Let z = a + ib, b ≠ 0 be complex numbers satisfying z ^ 2 = ¯ z · 2...

Let z=a+ib,b≠0z = a + ib, b \ne 0 be complex numbers satisfying z2=z¯⋅21−∣z∣{z}^{2} = \overset{¯}{z} \cdot {2}^{1 - \left|z\right|}. Then the least value of n∈Nn \in N, such that zn=(z+1)n{z}^{n} = {\left(z + 1\right)}^{n}, is equal to _____ .

Correct answer

0

Step-by-step solution

Given,

z2=z¯⋅21−∣z∣⋯(1){z}^{2} = \overset{¯}{z} \cdot {2}^{1 - \left|z\right|} ⋯ \left(1\right)

On taking modulus both side we get,

⇒∣z∣2=∣z∣⋅21−∣z∣⇒ {\left|z\right|}^{2} = \left|z\right| \cdot {2}^{1 - \left|z\right|}

⇒∣z∣=21−∣z∣,∵b≠0⇒∣z∣≠0⇒ \left|z\right| = {2}^{1 - \left|z\right|}, ∵ b \ne 0 ⇒ \left|z\right| \ne 0

So comparing both side we get ∣z∣=1⋯\left|z\right| = 1 ⋯\left(2\right)</p><p>Nowputting</p><p>Now puttingz = a + ibthenthen\sqrt{{a}^{2} + {b}^{2}} = 1 ⋯ \left(3\right)</p><p>Nowagainfromequation(1)</p><p>Now again from equation \left(1\right), equation \left(2\right),equation(3), equation \left(3\right) we get:

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

Now on comaparing imagenary and real part we get,

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

Now solving we get, a=−12a = - \dfrac{1}{2} and b=±32b = \pm \dfrac{\sqrt{3}}{2}

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

Now solving zn=(z+1)n⇒(z+1z)n=1{z}^{n} = {\left(z + 1\right)}^{n} ⇒ {\left(\dfrac{z + 1}{z}\right)}^{n} = 1

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

⇒(1+3i2)n=1⇒ {\left(\dfrac{1 + \sqrt{3}i}{2}\right)}^{n} = 1

⇒(−ω2)n=1⇒ {\left(- {\omega}^{2}\right)}^{n} = 1, then minimum value of nn is 66

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