Problem 19 - Algebra and Trigonometry

Question

\(17-24=\) Sketch the set in the complex plane. $$ \\{z| | z |=3\\} $$

Step-by-Step Solution

Answer

The set is a circle of radius 3 centered at the origin in the complex plane.

Step 1: Analyze the Set Notation

The given set \(\{z \ | \ |z| = 3\}\) specifies all complex numbers \(z\) whose modulus is 3.

Step 2: Understand Modulus in the Complex Plane

In the complex plane, the modulus of a complex number \(z = a + bi\) is given by \(|z| = \sqrt{a^2 + b^2}\). A constant modulus forms a circle centered at the origin.

Step 3: Sketch the Circle

Since \(|z| = 3\) represents all points at a distance of 3 from the origin, it's a circle with radius 3 centered at the origin in the complex plane. To sketch it, imagine a circle centered at the origin, with every point on the circle having a distance of 3 from (0,0).

Key Concepts

Modulus of Complex Number

When we talk about the modulus of a complex number, we refer to its size or magnitude. A complex number is generally represented as \(z = a + bi\), where \(a\) is the real part and \(b\) is the imaginary part. To find how 'long' this complex number is from the origin on the complex plane, we use the modulus. This can be thought of like finding the length of a vector.The modulus is calculated using the formula:

• \(|z| = \sqrt{a^2 + b^2}\)

This formula comes from the Pythagorean theorem. The real part \(a\) and the imaginary part \(b\) act like the two legs of a right triangle. Therefore, the modulus is simply the hypotenuse, the straight line distance from the origin \((0,0)\) to the point \((a,b)\).This is why the modulus is always a positive real number, as it represents a distance, not a direction or a vector.

Circle in Complex Plane

A circle in the complex plane can be visualized with ease thanks to the modulus of a complex number. When we specify that the modulus of a complex number \(|z|\) is a constant, like 3, we are indicating a particular set of points.

• Each point is at the same distance from the origin.
• That distance is the radius of the circle.

For example, \(\{z \ | \ |z| = 3\}\) describes all points (complex numbers) that are exactly 3 units away from the origin \((0,0)\). Sketching this involves picturing or drawing a circle where every point on the circle is the same distance, in this case, a radius of 3. Just like in geometry, this defines a perfect circle, demonstrating how beautifully geometry intertwines with algebra in the complex plane.

Complex Numbers

Complex numbers are at the core of mathematics and engineering because they give us an advanced, yet understandable way to manage problems involving two dimensions. A standard complex number takes the form \(z = a + bi\), where \(a\) and \(b\) are real numbers.

• \(a\) is called the 'real part'.
• \(b\) is the 'imaginary part', where \(i = \sqrt{-1}\).

Complex numbers go beyond real numbers by incorporating both dimensions: the real and the imaginary. This can be visualized on the complex plane, which resembles a coordinate plane.

• The horizontal axis is the real part.
• The vertical axis is the imaginary part.

Together, these give the complex plane its unique and powerful capabilities. Complex numbers simplify calculations involving rotations and oscillations in physical systems, making them indispensable in various fields like electrical engineering and quantum physics.