Circle in Complex Form

Rarely Tested

Circle in Complex Form

## Formula

A circle with centre $z_0$ and radius $$r$$ is:

$$|z-z_0|=r$$

If:

$$z_0=a+ib$$

then:

$$|z-(a+ib)|=r$$

In Cartesian coordinates:

$$(x-a)^2+(y-b)^2=r^2$$

## Usage

- Used to convert between complex and Cartesian equations of circles.

Question 1

If $$z = re^{i\theta}$$ is a complex number such that $$|z - 1| = 1$$ and $$|z - i| = 1,$$ find $$|z|.$$

Question 2

 Let $$z_1, z_2,$$ and $$z_3$$ be three distinct complex numbers satisfying $$|z_1| = |z_2| = |z_3| = 2$$. Find the maximum possible value of the expression:

$$|z_1 - z_2| \cdot |z_2 - z_3| \cdot |z_3 - z_1|$$

    Question 3

    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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