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Complex Numbers and Quadratic Equations · Question 48

JEE Main 2025 (Online) 4th April Evening ShiftNumericalMedium📈 Topic in 16% papers+4
1

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

Answer

11

Solution

x2+x+1=0 = or 2, so 3=1 and 1+ + 2=0

( k+ 1 k )2= 2k+ -2k+2

If k is a multiple of 3: 2k= -2k=1 term =1+1+2=4

Otherwise: 2k+ -2k= 2k+ k=-1 term =-1+2=1

every block of three terms (k=3r-2, 3r-1, 3r) gives 1+1+4=6

k=1 to 9: 3 6=18; k=10: 18+1=19; k=11: 19+1=20

n=11

Answer: 11

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Keep practising — Complex Numbers and Quadratic Equations

2

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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3

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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4

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
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5

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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6

Let z be a complex number such that |z| = 1. If 2 + k2 zk + z = kz, k R, then the maximum distance of k + ik2 from the circle |z - (1 + 2i)| = 1 is :

  1. 5 + 1
  2. 3
  3. 3 + 1
  4. 2
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7

Let Pn = n + n, n N. If P10 = 123, P9 = 76, P8 = 47 and P1 = 1, then the quadratic equation having roots 1 and 1 is :

  1. x2 + x - 1 = 0
  2. x2 - x + 1 = 0
  3. x2 + x + 1 = 0
  4. x2 - x - 1 = 0
JEE Main 2025 (Online) 2nd April Morning Shift
8

If the set of all a R - \1\, for which the roots of the equation (1 - a)x2 + 2(a - 3)x + 9 = 0 are positive is (- , - ] [ , ), then 2 + + is equal to .

JEE Main 2025 (Online) 2nd April Evening Shift
9

The number of solutions of the equation ( 9x - 9 x + 2 ) ( 2x - 7 x + 3 ) = 0 is :

  1. 3
  2. 2
  3. 1
  4. 4
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10

Let |z1 - 8 - 2i| 1 and |z2 - 2 + 6i| 2, z1, z2 C. Then the minimum value of |z1 - z2| is :

  1. 3
  2. 10
  3. 7
  4. 13
JEE Main 2025 (Online) 29th January Morning Shift
11

The sum, of the squares of all the roots of the equation x2 + |2x - 3| - 4 = 0, is

  1. 6(2 - 2)
  2. 3(3 - 2)
  3. 3(2 - 2)
  4. 6(3 - 2)
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