Distance-Based Loci

Rarely Tested

Distance-Based Loci

## Formula

$$|z-z_1|=k$$

represents a circle with centre $z_1$ and radius $$k$$.

$$|z-z_1|=|z-z_2|$$

represents the perpendicular bisector of the segment joining $z_1$ and $z_2$.

$$|z-z_1|<k$$

represents the interior of a circle.

$$|z-z_1|>k$$

represents the exterior of a circle.

## Conditions / Special Cases

For:

$$|z-z_1|\le k$$

the locus is the closed circular region.

For:

$$|z-z_1|\ge k$$

the locus is the exterior including the boundary.

## Usage

- Used to interpret inequalities involving complex moduli geometrically.

Question 1

If $$z$$ is a complex number satisfying $$\left|\frac{z-2}{z+2}\right|=1,$$ then the  minimum value of $$|z|^2-4\operatorname{Re}(z)$$ is ______.

Question 2

If $$z = x + iy$$ satisfies $$|z - 4| = |z + 4|$$, then the locus of $$z$$ is a straight line. The number of lattice points (points with integer coordinates) on this line strictly inside the circle $$|z| = 6$$ is:

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