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Complex Numbers and Quadratic Equations · Question 55

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1

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 .

Answer

7

Solution

Both roots positive needs (i) real roots, (ii) sum > 0, (iii) product > 0.

(i) D 0: 4(a - 3)2 - 36(1 - a) 0

a2 - 6a + 9 - 9 + 9a 0 a(a + 3) 0

a -3 or a 0

(iii) Product = 91 - a > 0 a < 1

(ii) Sum = -2(a - 3)1 - a = 2(3 - a)1 - a > 0, true for every a < 1

Combining: a (- , -3] [0, 1)

= 3, = 0, = 1

2 + + = 6 + 0 + 1 = 7

Answer: 7

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Keep practising — Complex Numbers and Quadratic Equations

2

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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3

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
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4

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)
JEE Main 2025 (Online) 28th January Morning Shift
5

Let O be the origin, the point A be z1 = 3 + 2 2i, the point B(z2) be such that 3|z2| = |z1| and (z2) = (z1) + 6. Then

  1. area of triangle ABO is 114
  2. area of triangle ABO is 11 3
  3. ABO is a scalene triangle
  4. ABO is an obtuse angled isosceles triangle
JEE Main 2025 (Online) 28th January Morning Shift
6

If + i and + i are the roots of x2 - (3 - 2i)x - (2i - 2) = 0, i = -1, then + is equal to:

  1. 2
  2. -6
  3. 6
  4. -2
JEE Main 2025 (Online) 28th January Evening Shift

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