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JEE Main 202313 AprilEvening Shift
Exam
JEE Main
Year
2023
Date
13 April
Shift
Evening Shift
Subject
Mathematics
Chapter
Complex Number

JEE Main 2023 · 13 April · Evening Shift · Mathematics · Complex Number

Let S = \ z ∈ ℂ: ¯ z = i( z ^ 2 + Re ( ¯ z ))\ . Then ∑ _ z ∈ S | z...

Let S={z∈C:z¯=i(z2+Re(z¯))}S = \left\{z \in \mathbb{C}: \overset{¯}{z} = i\left({z}^{2} + Re ( \overset{¯}{z} )\right)\right\}. Then ∑z∈S∣z∣2\mathop{∑}_{z \in S} | z{|}^{2} is equal to

Options

  1. A52\dfrac{5}{2}
  2. B44
  3. C72\dfrac{7}{2}
  4. D33

Correct answer

B. 44

Step-by-step solution

Given,

z¯=i(z2+Re(z¯))</p><p>Now,let\overset{¯}{z} = i \left({z}^{2} + Re ( \overset{¯}{z} )\right)</p><p>Now, letz = x + iy,so, so\overset{¯}{z} = x - iy</p><p>Nowputtingthevaluein,</p><p>Now putting the value in,\overset{¯}{z} = i \left({z}^{2} + Re ( \overset{¯}{z} )\right)weget,</p><p>we get,</p><p>\overset{¯}{z} = i \left({z}^{2} + Re ( \overset{¯}{z} )\right)

⇒x−iy=i(x2−y2+2ixy+x)⇒ x - iy = i \left({x}^{2} - {y}^{2} + 2ixy + x\right)

⇒x−iy=i(x2−y2+x)−2xy⇒ x - iy = i\left({x}^{2} - {y}^{2} + x\right) - 2xy

Now comparing real part we get,

⇒x=−2xy⇒x(2y+1)=0⇒ x = - 2xy ⇒ x ( 2y + 1 ) = 0

⇒x=0,y=−12.....(1)⇒ x = 0, y = \dfrac{- 1}{2} . . . . . \left(1\right)

And imaginary part we get,

−y=x2−y2+x.......(2)</p><p>NowtakingCase(I)when- y = {x}^{2} - {y}^{2} + x . . . . . . . \left(2\right)</p><p>Now taking Case (I) whenx = 0 in equation(2)weget,</p><p>equation \left(2\right) we get,</p><p>⇒ - y = - {y}^{2}</p><p></p><p>⇒ {y}^{2} - y = 0 ⇒ y = 0, 1</p><p>So,</p><p>So,z = 0, i</p><p>NowtakingCase(II)when</p><p>Now taking Case (II) wheny = −12\dfrac{- 1}{2} in equation\left(2\right) we get,

⇒⇒\dfrac{1}{2} =x2−{x}^{2} -\dfrac{1}{4} +xx

⇒x2+x−⇒ {x}^{2} + x -\dfrac{3}{4} =00

⇒4x+4x−3=0⇒ 4x + 4x - 3 = 0

⇒(2x−1)(2x+3)=0⇒ ( 2x - 1 ) ( 2x + 3 ) = 0

⇒x=⇒ x =\dfrac{1}{2},,\dfrac{- 3}{2}

So, z=z =\dfrac{1}{2} - \dfrac{1}{2}i,i,\dfrac{- 3}{2} - \dfrac{1}{2}ii

Now finding, ∑∣z∣2=0+1+∑ | z{|}^{2} = 0 + 1 +\dfrac{1}{2} + \dfrac{5}{2} =44

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