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Complex Numbers and Quadratic Equations · Question 42

JEE Main 2025 (Online) 7th April Evening ShiftMCQMedium📈 Topic in 45% papers+4−1
1

If the locus of z C, such that Re ( z-12z+i ) + Re ( z-12 z-i ) = 2, is a circle of radius r and center (a, b), then 15abr2 is equal to :

  1. 16
  2. 24
  3. 12
  4. 18

Answer

(4) 18

Solution

z-12 z-i = ( z-12z+i ), and a number and its conjugate have the same real part.

2 Re ( z-12z+i ) = 2 Re ( z-12z+i ) = 1

Put z = x + iy:

(x-1) + iy2x + i(2y+1), real part = 2x(x-1) + y(2y+1)4x2 + (2y+1)2

2x2 - 2x + 2y2 + y = 4x2 + 4y2 + 4y + 1

2x2 + 2y2 + 2x + 3y + 1 = 0

x2 + y2 + x + 32y + 12 = 0

Centre (a, b) = (- 12, - 34 )

r2 = 14 + 916 - 12 = 516

15abr2 = 15 38 516 = 18

Answer: (4)

JEE Main 2025 (Online) 7th April Evening Shift

Keep practising — Complex Numbers and Quadratic Equations

2

The number of real roots of the equation x|x-2| + 3|x-3| + 1 = 0 is :

  1. 4
  2. 3
  3. 2
  4. 1
JEE Main 2025 (Online) 7th April Evening Shift
3

For t > -1, let t and t be the roots of the equation ((t + 2)1/7 - 1 )x2 + ((t + 2)1/6 - 1 )x + ((t + 2)1/21 - 1 ) = 0 If t -1+ t = a and t -1+ t = b, then 72(a + b)2 is equal to .

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4

Consider the equation x2 + 4x - n = 0, where n [20, 100] is a natural number. Then the number of all distinct values of n, for which the given equation has integral roots, is equal to

  1. 6
  2. 5
  3. 8
  4. 7
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5

Let A = \z C : |z - 2 - i| = 3\, B = \z C : Re(z - iz) = 2\ and S = A B. Then z S |z|2 is equal to .

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6

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  1. 130
  2. 150
  3. 160
  4. 140
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7

If is a root of the equation x2+x+1=0 and k=1n ( k+ 1 k )2=20, then n is equal to .

JEE Main 2025 (Online) 4th April Evening Shift
8

Let and be the roots of x2 + 3x - 16 = 0, and and be the roots of x2 + 3x - 1 = 0. If Pn = n + n and Qn = n + n, then P25 + 3P242P23 + Q25 - Q23Q24 is equal to

  1. 4
  2. 3
  3. 5
  4. 7
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9

Let z C be such that z2+3iz-2+i = 2+3i. Then the sum of all possible values of z2 is :

  1. -19+2i
  2. -19-2i
  3. 19-2i
  4. 19+2i
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10

If z1, z2, z3 C are the vertices of an equilateral triangle whose centroid is z0, then k=13 (zk - z0)2 is equal to

  1. 0
  2. 1
  3. i
  4. -i
JEE Main 2025 (Online) 3rd April Evening Shift
11

Let the equation x(x + 2)(12 - k) = 2 have equal roots. Then the distance of the point (k, k2 ) from the line 3x + 4y + 5 = 0 is

  1. 15
  2. 12
  3. 5 3
  4. 15 5
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