Question

Describe geometrically the set of points in the complex plane satisfying the following equations. 51\. \(|z|=2\)

Short answer

The equation \(|z| = 2\) represents a circle centered at the origin with radius 2 in the complex plane.

Step-by-step solution

- Understand the modulus of a complex number

In the complex plane, any complex number can be written as \(z = x + yi\), where \(x\) and \(y\) are real numbers, and \(i\) is the imaginary unit with \(i^2 = -1\). The modulus of a complex number \(z\) is given by \[|z| = \sqrt{x^2 + y^2}\].

- Interpret the given equation

Given the equation \(|z| = 2\), this translates to the condition that the distance of the complex number \(z = x + yi\) from the origin \((0, 0)\) in the complex plane is 2.

- Represent geometrically

Geometrically, the set of points that are at a constant distance from a fixed point forms a circle. Since the modulus of \(z\) is 2, all points \(z\) that are 2 units away from the origin lie on a circle centered at the origin with radius 2.

- Draw the conclusion

Thus, the equation \(|z| = 2\)\ represents a circle in the complex plane. The center of this circle is the origin \((0, 0)\), and the radius is 2.

Key concepts

Modulus of a Complex Number

When dealing with complex numbers, the modulus is a fundamental concept. The modulus of a complex number is essentially a measure of its 'size' or 'distance' from the origin on the complex plane. If you have a complex number written as \(z = x + yi\), where \(x\) and \(y\) are real numbers, the modulus, represented as \(|z|\), is calculated using the formula: \[|z| = \sqrt{x^2 + y^2}\]\.
This formula originates from the Pythagorean Theorem, as it treats the complex number as a point \( (x, y) \) in a two-dimensional coordinate system. Here, \( x \) is the real part and \( y \) is the imaginary part.

• Example: For a complex number \( z = 3 + 4i \), the modulus would be \[|z| = \sqrt{3^2 + 4^2} = \sqrt{9 + 16} = 5\]

The modulus provides a geometric interpretation, making it crucial for understanding distances and other properties in complex plane geometry.

Distance in the Complex Plane

Distance in the complex plane can be visualized just like distances in the regular Cartesian plane. If you have two points, \(z_1 = x_1 + y_1i \) and \(z_2 = x_2 + y_2i\), the distance between them is given by the difference of their corresponding points.
The formula for the distance is derived from the modulus: \[d = |z_1 - z_2| = \sqrt{(x_1 - x_2)^2 + (y_1 - y_2)^2}\]\.

• Example: If \(z_1 = 1 + i \) and \(z_2 = 4 + 5i\), their distance would be \[|z_1 - z_2| = |(1 - 4) + (1 - 5)i| = |(-3) + (-4)i| = \sqrt{(-3)^2 + (-4)^2} = \sqrt{9 + 16} = 5\]

Understanding this distance formula helps in grasping more complex geometric concepts in the plane of complex numbers. It parallels the regular distance formula learned in basic geometry, making it familiar and easy to understand.

Geometric Representation of Complex Numbers

In the complex plane, each complex number corresponds to a specific point. These points can be plotted on a two-dimensional plane where:

• The x-axis represents the real part of the complex number.
• The y-axis represents the imaginary part.

For instance, consider the equation \(|z|=2\). Here, \(|z|\) represents the modulus of a complex number \(z = x + yi\). Given that \(|z| \)// = 2, this means all points \(z\) are 2 units away from the origin.
Geometrically, these points will form a circle centered at the origin with a radius of 2. Any point on this circle represents a complex number whose modulus is 2.

• Understanding that a fixed modulus results in a circle helps in interpreting complex numbers geometrically. This visual aid makes it easier to grasp more abstract concepts in complex analysis.
  

By breaking down the geometric representation, you can better understand transformations, mappings, and other advanced topics in complex numbers.