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JEE Main 202329 JanuaryEvening Shift
Exam
JEE Main
Year
2023
Date
29 January
Shift
Evening Shift
Subject
Mathematics
Chapter
Complex Number

JEE Main 2023 · 29 January · Evening Shift · Mathematics · Complex Number

Let α = 8 - 14i, A = \ z ∈ ℂ: - ¯ α ¯ z z ^ 2 - ( ¯ z ) ^ 2 - 112i...

Let α=8−14i,A={z∈C:\alphaz−α¯z¯z2−(z¯)2−112i=1}\alpha = 8 - 14i, A = \left\{z \in \mathbb{C}: \dfrac{\alphaz - \overset{¯}{\alpha}\overset{¯}{z}}{{z}^{2} - ( \overset{¯}{z}{)}^{2} - 112i} = 1\right\} and B={z∈C:∣z+3i∣=4}B = \left\{z \in \mathbb{C}: \left|z + 3i\right| = 4\right\}

Then, ∑z∈A∩B(Rez−Imz)\mathop{∑}_{z \in A \cap B} ( Re z - Imz ) is equal to ________

Correct answer

0

Step-by-step solution

Given:

A={z∈C:\alphaz−α¯z¯z2−(z¯)2−112i=1}A = \left\{z \in \mathbb{C}: \dfrac{\alphaz - \overset{¯}{\alpha}\overset{¯}{z}}{{z}^{2} - ( \overset{¯}{z}{)}^{2} - 112i} = 1\right\}

B={z∈C:∣z+3i∣=4}B = \left\{z \in \mathbb{C}: \left|z + 3i\right| = 4\right\}

α=8−14i\alpha = 8 - 14i

Let

z=x+iyz = x + iy

So,

\alphaz=(8−14i)(x+iy)\alphaz = \left(8 - 14i\right)\left(x + iy\right)

⇒\alphaz=(8x+14y)+i(−14x+8y)⇒ \alphaz = ( 8x + 14y ) + i ( - 14x + 8y )

Also,

z+z¯=2xandz + \overset{¯}{z} = 2x andz - \overset{¯}{z} = 2iy</p><p>SetA:</p><p></p><p>Set A:</p><p>\dfrac{\alphaz - \overset{¯}{\alpha}\overset{¯}{z}}{{z}^{2} - ( \overset{¯}{z}{)}^{2} - 112i} = 1</p><p></p><p>⇒ \dfrac{2i\left(- 14x + 8y\right)}{\left(z + \overset{¯}{z}\right)\left(z - \overset{¯}{z}\right) - 112i} = 1</p><p></p><p>⇒ \dfrac{2i\left(- 14x + 8y\right)}{4ixy - 112i} = 1</p><p></p><p>⇒ \dfrac{- 14x + 8y}{\left(2xy - 56\right)} = 1</p><p></p><p>⇒ xy + 7x - 4y - 28 = 0</p><p></p><p>⇒ \left(x - 4\right)\left(y + 7\right) = 0</p><p></p><p>⇒ x = 4orory = - 7</p><p>Set</p><p>SetB:</p><p>∣z+3i∣=4:</p><p>\left|z + 3i\right| = 4

⇒∣x+i(y+3)∣=4⇒ \left|x + i\left(y + 3\right)\right| = 4

⇒x2+(y+3)2=16⇒ {x}^{2} + {\left(y + 3\right)}^{2} = 16

When x=4⇒y=−3x = 4 ⇒ y = - 3

When y=−7⇒x=0y = - 7 ⇒ x = 0

∴A∩B={4−3i,0−7i}∴ A \cap B = \left\{4 - 3i, 0 - 7i\right\}

So, ∑z∈A∩B(Rez−Imz)=4−(−3)+(0−(−7))=14\mathop{∑}_{z \in A \cap B}\left(Rez - Im z\right) = 4 - ( - 3 ) + ( 0 - ( - 7 ) ) = 14

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