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JEE Main 202225 JulyMorning Shift
Exam
JEE Main
Year
2022
Date
25 July
Shift
Morning Shift
Subject
Mathematics
Chapter
Complex Number

JEE Main 2022 · 25 July · Morning Shift · Mathematics · Complex Number

For n ∈ N , let S _ n = \ z ∈ C: |z - 3 + 2i| = (n)/(4)\ and T _ n...

For n∈Nn \in N, let Sn={z∈C:∣z−3+2i∣=n4}and{S}_{n} = \left\{z \in C: \left|z - 3 + 2i\right| = \dfrac{n}{4}\right\} and{T}_{n} = \left\{z \in C: \left|z - 2 + 3i\right| = \dfrac{1}{n}\right\}.Thenthenumberofelementsintheset{n∈N:Sn∩Tn=ϕ}. Then the number of elements in the set \left\{n \in N: {S}_{n} \cap {T}_{n} = ϕ\right\} is

Options

  1. A00
  2. B22
  3. C33
  4. D44

Correct answer

D. 44

Step-by-step solution

Here Sn:∣z−(3−2i)∣=n4{S}_{n}: \left|z - \left(3 - 2i\right)\right| = \dfrac{n}{4} represents a circle with center C1(3,−2){C}_{1}\left(3, - 2\right) and radius n4\dfrac{n}{4}

and Tn:∣z−(2−3i)∣=1n{T}_{n}: \left|z - \left(2 - 3i\right)\right| = \dfrac{1}{n} represents a circle with center C2(2,−3){C}_{2}\left(2, - 3\right) and radius 1n\dfrac{1}{n}

For Sn∩Tn=ϕ{S}_{n} \cap {T}_{n} = ϕ, both circles do not intersect each other.

When C1C2>n4+1n{C}_{1}{C}_{2} > \dfrac{n}{4} + \dfrac{1}{n}

i.e. 2>n4+1n\sqrt{2} > \dfrac{n}{4} + \dfrac{1}{n}
then possible values of n=1,2,3,4n = 1, 2, 3, 4

When C1C2<∣n4−1n∣{C}_{1}{C}_{2} < \left|\dfrac{n}{4} - \dfrac{1}{n}\right|

⇒2<∣n2−44n∣⇒ \sqrt{2} < \left|\dfrac{{n}^{2} - 4}{4n}\right|

then nn has infinite solutions for n∈Nn \in N

Hence, there are total four values possible.

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