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Complex Numbers and Quadratic Equations · Question 46

JEE Main 2025 (Online) 4th April Morning ShiftNumericalMedium📈 Topic in 45% papers+4
1

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 .

Answer

22

Solution

Let z = x + iy.

A: |z - (2 + i)| = 3 (x - 2)2 + (y - 1)2 = 9

B: z - iz = (x + iy) - i(x + iy) = (x + y) + i(y - x)

Re(z - iz) = x + y = 2 y = 2 - x

Substituting in A: (x - 2)2 + (1 - x)2 = 9

2x2 - 6x - 4 = 0 x2 - 3x - 2 = 0

Two points: x1 + x2 = 3, x1x2 = -2 x12 + x22 = 9 + 4 = 13

|z|2 = x2 + (2 - x)2 = 2x2 - 4x + 4

|z|2 = 2(x12 + x22) - 4(x1 + x2) + 8

= 26 - 12 + 8 = 22

Answer: 22

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3

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