Related Formula
Magnitude squared representation:
|z|² = x² + y² for z = x + iy$$|z|^2 = x^2 + y^2 \quad \text{for } z = x + iy$$
Core Logic
Convert complex sets into Cartesian forms by setting z = x + iy$z = x + iy$:
Set A$A$: |(x-2) + i(y-1)| = 3 (x-2)² + (y-1)² = 9 (1)$|(x-2) + i(y-1)| = 3 \implies (x-2)^2 + (y-1)^2 = 9 \quad \dots (1)$
Set B$B$: z - iz = (x+iy) - i(x+iy) = (x+y) + i(y-x)$z - iz = (x+iy) - i(x+iy) = (x+y) + i(y-x)$.
Re(z - iz) = 2 x + y = 2 y = 2 - x (2)$\operatorname{Re}(z - iz) = 2 \implies x + y = 2 \implies y = 2 - x \quad \dots (2)$
Step 1: Solve System Algebraically
Substitute (2) into (1):
(x - 2)² + (2 - x - 1)² = 9 (x - 2)² + (1 - x)² = 9$$(x - 2)^2 + (2 - x - 1)^2 = 9 \implies (x - 2)^2 + (1 - x)^2 = 9$$
x² - 4x + 4 + 1 - 2x + x² = 9 2x² - 6x - 4 = 0 x² - 3x - 2 = 0$$x^2 - 4x + 4 + 1 - 2x + x^2 = 9 \implies 2x^2 - 6x - 4 = 0 \implies x^2 - 3x - 2 = 0$$
Roots are x1,2 = 3 ± √(17)2$x_{1,2} = \frac{3 \pm \sqrt{17}}{2}$.
Correspondingly, y = 2 - x y1,2 = 1 ∓ √(17)2$y = 2 - x \implies y_{1,2} = \frac{1 \mp \sqrt{17}}{2}$.
Step 2: Evaluate Sum of Square Magnitudes
Since S$S$ consists of the two intersection points z₁, z₂$z_1, z_2$:
Σz in S |z|² = (x₁² + y₁²) + (x₂² + y₂²) = (x₁² + x₂²) + (y₁² + y₂²)$$\sum_{z \in S} |z|^2 = (x_1^2 + y_1^2) + (x_2^2 + y_2^2) = (x_1^2 + x_2^2) + (y_1^2 + y_2^2)$$
Using identities from quadratic equation x² - 3x - 2 = 0$x^2 - 3x - 2 = 0$ (x₁+x₂ = 3, x₁x₂ = -2$x_1+x_2 = 3, x_1x_2 = -2$):
x₁² + x₂² = (3)² - 2(-2) = 13$x_1^2 + x_2^2 = (3)^2 - 2(-2) = 13$.
Since y = 2-x$y = 2-x$, y² = 4 - 4x + x² y₁² + y₂² = 8 - 4(3) + 13 = 9$y^2 = 4 - 4x + x^2 \implies y_1^2 + y_2^2 = 8 - 4(3) + 13 = 9$.
Σz in S |z|² = 13 + 9 = 22$$\sum_{z \in S} |z|^2 = 13 + 9 = 22$$
Pattern Recognition
Avoid explicitly using radical root approximations. Summing symmetric expressions directly through standard Vieta coefficient sum shortcuts preserves clean fractions.
Chapter Mix
Class 11 Mathematics: Complex Numbers and Quadratic Equations