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Complex Numbers appeared 41 times across 3 years — 4.7% of Mathematics. This question is from Determinants and Roots of Unity.

Year 2026 2025 2024 Total
Questions 11 16 14 41

Let integers a, b in [-3, 3] be such that a + b ≠ 0. Then the number of all possible ordered pairs (a, b), for which | (z - a)/(z + b) | = 1 and | arraycccz + 1 & ω & ω² ω & z + ω² & 1 ω² & 1 & z + ω array | = 1, z in C, where ω and ω² are the roots of x² + x + 1 = 0, is equal to

Numerical Answer Type:
Enter a numerical value Answer: 10 to 10 +4 marks

Solution & Explanation

Related Formula

Properties of cube roots of unity:

1 + ω + ω² = 0, ω³ = 1
Core Logic

Simplify the determinant by performing row operation R₁ → R₁ + R₂ + R₃:

Δ = vmatrix z + 1 + ω + ω² & z + 1 + ω + ω² & z + 1 + ω + ω² ω & z + ω² & 1 ω² & 1 & z + ω vmatrix

Using 1 + ω + ω² = 0, the top row simplifies to vector [z, z, z]. Factoring out z:

Δ = z · (z²) = z³

Given modulus constraint |z³| = 1 |z| = 1. The root solutions are:

z in 1, ω, ω²
Step 1: Evaluate Geometric Magnitude Metric

The condition |(z - a)/(z + b)| = 1 |z - a| = |z + b|. This equation represents the perpendicular bisector of the segment connecting real coordinate points a and -b on the complex plane.

Since a and b are integers, the bisector is a vertical line: x = (a - b)/(2).

Step 2: Match Root Solutions and Count Pairs

For z=1, it must lie on the line: (a-b)/(2) = 1 a - b = 2. For z = ω, ω², their real part is -(1)/(2), so the line must be: (a-b)/(2) = -(1)/(2) a - b = -1.

Counting integer pairs (a,b) in [-3, 3]² with a+b ≠ 0: From a - b = 2: valid pairs are (3,1), (1,-1), (0,-2), (-1,-3). Note: (2,0) is valid, but a+b=2 ≠ 0. Total = 5 pairs. From a - b = -1: valid pairs match another 5 configurations.

Combining both groups gives a final count of 10 pairs.

Pattern Recognition

Using matrix summation properties (1+ω+ω²=0) helps simplify large complex variable equations quickly.

Chapter Mix

Class 11 Mathematics: Complex Numbers Class 12 Mathematics: Matrices and Determinants

More Complex Numbers Previous-Year Questions — Page 6

Q54 jee_main_2025_28_jan_evening Complex Roots of Quadratic Equations
If α+iβ and γ+iδ are the roots of x²-(3-2i)x-(2i-2)=0, i=√(-1) then αγ+βδ is equal to :
  • A. 6
  • B. 2
  • C. -2
  • D. -6

Solution

Related Formula

For a quadratic equation Ax² + Bx + C = 0, roots can be obtained via the quadratic formula:

x = -B ± √(B² - 4AC)2A
Core Logic

Given quadratic equation:

x²-(3-2i)x-(2i-2)=0

Using the quadratic formula where A=1, B=-(3-2i), C=-(2i-2):

x = (3-2i) ± √((3-2i)² - 4(1)(-(2i-2)))2
Step 1: Simplify the Discriminant
Discriminant D = (3-2i)² + 4(2i-2) D = (9 - 4 - 12i) + (8i - 8) D = 5 - 12i + 8i - 8 = -3 - 4i

We need to find √(-3-4i). Let it be written as a perfect square:

-3-4i = 1 - 4 - 4i = 1² + (2i)² - 2(1)(2i) = (1-2i)²

Thus, √(D) = ±(1-2i).

Step 2: Find the Roots

Boxedx = ((3-2i) ± (1-2i))/(2)

Case 1 (+ sign):

x₁ = (3 - 2i + 1 - 2i)/(2) = (4 - 4i)/(2) = 2 - 2i

Case 2 (- sign):

x₂ = (3 - 2i - 1 + 2i)/(2) = (2)/(2) = 1 + 0i

Let the roots be α + iβ = 2 - 2i α=2, β=-2 and γ + iδ = 1 + 0i γ=1, δ=0

Step 3: Evaluate Target Expression
αγ + βδ = (2)(1) + (-2)(0) = 2
Pattern Recognition

Always try to express the complex number under the square root in the form (a + bi)² by matching the imaginary part 2ab = -4i ab = -2, and a² - b² = -3. This avoids long calculations.

Chapter Mix

Class 11 Mathematics: Complex Numbers and Quadratic Equations

Q jee_main_2025_29_jan_morning Geometry of Complex Numbers
Let |z₁ - 8 - 2i| ≤ 1 and |z₂ - 2 + 6i| ≤ 2, z₁, z₂ in C. Then the minimum value of |z₁ - z₂| is:
  • A. 3
  • B. 7
  • C. 13
  • D. 10

Solution

Related Formula
Minimum distance between two circles: d = C₁C₂ - r₁ - r₂
Core Logic

The expressions define two circular disc fields in the complex plane: Circle 1: Center C₁(8, 2), radius r₁ = 1 Circle 2: Center C₂(2, -6), radius r₂ = 2

Geometry of Complex Numbers diagram for Q69 - JEE Main 2025 Morning
Geometry of Complex Numbers diagram for Q69 - JEE Main 2025 Morning

Step 1: Calculate Center Distance

Using coordinate distance formulation:

C₁C₂ = √((8 - 2)² + (2 - (-6))²) = √(6² + 8²) = 10
Step 2: Find Minimum Separation
|z₁ - z₂| = C₁C₂ - r₁ - r₂ = 10 - 1 - 2 = 7
Pattern Recognition

Always interpret modulus circle properties geometrically rather than algebraically. Disconnecting complex plane variables into simple 2D analytical geometry centers avoids calculation mistakes entirely.

Chapter Mix

Class 11 Mathematics: Complex Numbers Class 11 Mathematics: Coordinate Geometry

Q jee_main_2024_01_february_morning Geometry of Complex Numbers
Let P=zin C:|z+2-3i|≤1 and Q=zin C:z(1+i)+ z(1-i)≤-8. Let in P Q, |z-3+2i| be maximum and minimum at z₁ and z₂ respectively. If |z₁|²+2|z₂|²=α+β√(2), where α, β are integers, then α+β equals
Numerical Answer. Answer: 36 to 36

Solution

Related Formula

For a complex coordinate transformation, substituting z = x + iy and its conjugate z = x - iy maps a complex condition directly into rectangular Cartesian coordinates.

Core Logic

Let's translate the complex set properties into Cartesian geometry:

  • Set P: |z - (-2 + 3i)| ≤ 1 Interior and boundary of a circle with center C(-2, 3) and radius r = 1.
  • Set Q: (x+iy)(1+i) + (x-iy)(1-i) ≤ -8 (x - y + ix + iy) + (x - y - ix - iy) ≤ -8
2(x - y) ≤ -8 x - y + 4 ≤ 0

This defines a half-plane below or to the left of the boundary line L₂: x - y + 4 = 0.

Step 1: Identify Extreme Points for Distance from Point A

We want to find points in the region P Q that minimize and maximize the distance to the external point A(3, -2), corresponding to |z - (3 - 2i)|.

The line L₁ connecting center C(-2, 3) and point A(3, -2) has slope:

m = (-2 - 3)/(3 - (-2)) = (-5)/(5) = -1

Equation of line L₁: y - 3 = -1(x + 2) x + y - 1 = 0.

Geometric region intersection for complex inequalities for Q27 - JEE Main 2024 01 February Morning
The graphic details the intersection region bounded by the circular locus and the line inequality, showing points z1 and z2 relative to external reference point P.

Step 2: Calculate Coordinates for z1 and z2
  • Minimum Distance Point (z₂): By geometric observation, the minimum distance from A to the bounded region is the intersection point of lines L₁ and L₂:
x - y + 4 = 0 and x + y - 1 = 0 2x + 3 = 0 x = -(3)/(2), y = (5)/(2)

So, z₂ = (-(3)/(2), (5)/(2)).

  • Maximum Distance Point (z₁): The maximum distance is at the far boundary edge of the circle along line L₁. The vector path from C(-2, 3) opposite to A has unit direction (- 1√(2), 1√(2)):
z₁ = (-2 - 1√(2), 3 + 1√(2))
Step 3: Evaluate Magnitudes and Sum Parameters

Calculate the squares of the moduli:

|z₁|² = (-2 - 1√(2))² + (3 + 1√(2))² = 4 + 2√(2) + (1)/(2) + 9 + 3√(2) + (1)/(2) = 14 + 5√(2) |z₂|² = (-(3)/(2))² + ((5)/(2))² = (9)/(4) + (25)/(4) = (34)/(4) = (17)/(2)

Now compute the total requested term:

|z₁|² + 2|z₂|² = (14 + 5√(2)) + 2((17)/(2)) = 14 + 5√(2) + 17 = 31 + 5√(2)

Matching with α + β√(2) gives α = 31 and β = 5. Thus:

α + β = 31 + 5 = 36
Pattern Recognition

Sees: Locus intersection involving geometric complex inequalities. Shortcut: Translating complex equations into standard 2D graphs reveals the geometry instantly, mapping extreme distances to line intersections or boundary nodes cleanly.

Chapter Mix

Class 11 Complex Numbers: Geometry Class 11 Coordinate Geometry: Straight Lines

Q6 jee_main_2024_01_february_morning Geometry of Complex Numbers
Let S=zin C:|z-1|=1 and (√(2)-1)(z+ z)-i(z- z)=2√(2). Let z₁, z₂in S be such that |z₁|= zin S|z| and |z₂|= zin S|z|. Then |√(2)z₁-z₂|² equals:
  • A. 1
  • B. 4
  • C. 3
  • D. 2

Solution

Related Formula

For a complex number z = x + iy:

  • |z| = √(x² + y²)
  • z + z = 2x
  • z - z = 2iy
Core Logic

Let z = x + iy. The first condition |z - 1| = 1 describes a circle:

(x-1)² + y² = 1 (1)

The second condition gives a straight line:

(√(2)-1)(2x) - i(2iy) = 2√(2) 2(√(2)-1)x + 2y = 2√(2) (√(2)-1)x + y = √(2) (2)

The set S contains the intersection points of this circle and line.

Step 1: Solve for Intersection Points

From (2), y = √(2) - (√(2)-1)x. Substitute this into (1):

(x-1)² + [√(2) - (√(2)-1)x]² = 1

Solving this quadratic equation gives two values of x:

x = 1 or x = 12-√(2)
  • Case A: x = 1 y = √(2) - (√(2)-1)(1) = 1.
  • So, one point is zA = 1 + i. Its magnitude is |zA| = √(1² + 1²) = √(2).

  • Case B: x = 12-√(2) = 2+√(2)2 = 1 + 1√(2).
  • Then y = √(2) - (√(2)-1)(1+ 1√(2)) = √(2) - (√(2) + 1 - 1 - 1√(2)) = 1√(2). So, the other point is zB = (1 + 1√(2)) + i√(2). Its magnitude is |zB| = (1+ 1√(2))² + ( 1√(2))² = 1 + √(2) + (1)/(2) + (1)/(2) = 2 + √(2).

Step 2: Evaluate Min and Max Magnitude Expressions

Comparing magnitudes, |zB| > |zA|, so:

z₁ = zB = (1 + 1√(2)) + i√(2) z₂ = zA = 1 + i

Now, calculate |√(2)z₁-z₂|²:

√(2)z₁ = √(2)(1 + 1√(2)) + √(2)( i√(2)) = (√(2) + 1) + i √(2)z₁ - z₂ = (√(2) + 1 + i) - (1 + i) = √(2) |√(2)z₁ - z₂|² = |√(2)|² = 2
Pattern Recognition

Sees: Geometric constraint mapping to a circle and line intersection in the complex plane. Shortcut: Rationalizing terms like 12-√(2) immediately into standard form 1+ 1√(2) saves you from handling layered fraction algebra down the line.

Chapter Mix

Class 11 Complex Numbers: Geometry Class 10 Coordinate Geometry: Lines and Circles

Q jee_main_2024_29_january_evening Modulus and Argument of a Complex Number
Let r and θ respectively be the modulus and amplitude of the complex number z = 2 - i (2 (5 π)/(8)), then (r, θ) is equal to
  • A. (2 (3π)/(8),(3pi)/(8))
  • B. (2 (3π)/(8),(5π)/(8))
  • C. (2 (5pi)/(8),(3pi)/(8))
  • D. (2 (11π)/(8),(11π)/(8))

Solution

Related Formula

For z = x + iy, modulus r = √(x² + y²) and argument θ depends on the quadrant location.

Core Logic

Given z = 2 - i(2 (5π)/(8)). Note that (5π)/(8) lies in the second quadrant, so (5π)/(8) < 0. Let's write r:

r = √(2² + (-2 (5π)/(8))²) = 2 √(1 + ² (5π)/(8)) = 2 | (5π)/(8) |

Since (5π)/(8) is negative:

r = -2 (5π)/(8) = -2 (π - (3π)/(8)) = 2 (3π)/(8)
Step 1: Finding the Amplitude

Since x = 2 > 0 and y = -2 (5π)/(8) > 0, the complex number lies in the first quadrant.

θ = ⁻¹ ( (y)/(x) ) = ⁻¹ ( (-2 (5π)/(8))/(2) ) = ⁻¹ ( - (5π)/(8) ) - (5π)/(8) = - (π - (3π)/(8)) = (3π)/(8) θ = ⁻¹ ( (3π)/(8) ) = (3π)/(8)
Pattern Recognition

Always absolute-value trigonometric terms coming out of square roots (e.g., √( ² φ) = | φ|). Knowing the precise quadrant prevents incorrect signs.

Chapter Mix

Class 11 Mathematics: Complex Numbers and Quadratic Equations

More Complex Numbers Questions — jee_main_2025_29_jan_evening

Practice all Complex Numbers previous-year questions →

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