JEE Main · Mathematics ↓ Falling

Complex Numbers appeared 41 times across 3 years — 4.7% of Mathematics. This question is from Geometry of Complex Numbers.

Year 2026 2025 2024 Total
Questions 11 16 14 41

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:

Solution & Explanation

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

Reference Study Guides

More Complex Numbers Previous-Year Questions — Page 9

Q26 jee_main_2024_31_jan_morning Properties of Modulus and Argument
If α denotes the number of solutions of |1 - i|^x = 2^x and β = ((|z|)/( (z))), where z = (π)/(4) (1 + i)⁴ ( 1 - √(π) i√(π) + i + √(π) - i1 + √(π) i), i = √(-1), then the distance of the point (α, β) from the line 4x - 3y = 7 is
Numerical Answer. Answer: 3 to 3

Solution

Core Logic
|1 - i|^x = 2^x (√(2))^x = 2^x 2x/2 = 2^x

This implies (x)/(2) = x x = 0. There is exactly 1 solution, so α = 1.

Step 1: Simplify complex number z
(1+i)⁴ = ((1+i)²)² = (1 + i² + 2i)² = (2i)² = -4

Thus, z = -π ( (1-√(π)i)(√(π)-i)π + 1 + (√(π)-i)(1-√(π)i)1 + π )

Step 2: Simplify Bracket

Let's expand the terms directly: z = (π)/(4)(-4) [ √(π) - π i - i - √(π)π + 1 + √(π) - i - π i - √(π)1 + π ]

= -π [ (-i(π+1))/(π+1) + (-i(π+1))/(π+1) ] = -π [ -i - i ] = 2π i
Step 3: Find beta

For z = 2π i: |z| = 2π and (z) = (π)/(2).

β = (|z|)/( (z)) = (2π)/(π/2) = 4
Step 4: Distance from Line

Distance of point (α, β) = (1, 4) from the line 4x - 3y - 7 = 0:

D = |4(1) - 3(4) - 7|√(4² + (-3)²) = (|4 - 12 - 7|)/(5) = (|-15|)/(5) = 3
Chapter Mix

Class 11 Maths: Complex Numbers and Quadratic Equations Class 11 Maths: Straight Lines

More Complex Numbers Questions — jee_main_2024_01_february_morning

Practice all Complex Numbers previous-year questions →

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