Chapter 2: Problem 13
Find the image of the given line under the complex mapping \(w=z^{2}\).\(y=x\)
Short Answer
Expert verified
The image is the imaginary axis with parabolic scaling \(v = 2u^2\).
Step by step solution
01
Understand the Problem
We need to find the image of the line described by the equation \(y = x\) when it is transformed by the complex mapping \(w = z^2\). This is a transformation in the complex plane.
02
Describe the Mapping
The complex mapping \(w = z^2\) means that for every complex number \(z = x + yi\), the image \(w\) is given by \(w = (x + yi)^2 = x^2 - y^2 + 2xyi\).
03
Set the Line Equation in Complex Form
In terms of complex numbers, the line \(y = x\) can be expressed as \(z = x + xi = x(1 + i)\). This represents all points in the form \(x(y = x)\) on the complex plane.
04
Apply the Mapping to the Line
Substitute \(z = x(1 + i)\) into the mapping \(w = z^2\). We get \(w = (x(1 + i))^2 = x^2(1 + i)^2 = x^2(-2i) = -2ix^2\).
05
Simplify the Image
The expression \(-2ix^2\) can be rewritten as \(w = 2x^2i\), where the real part is zero and the imaginary part is \(2x^2\). This means the image is purely imaginary.
06
Interpret the Result
The image of the line \(y = x\) under the transformation is the imaginary axis, scaled by \(2x^2\). Hence, for a given \(x\), the point \(w\) lies along the line \(v = 2u^2\) (where \(w = u + vi\) and \(u = 0\)). This results in a parabola opening along the imaginary axis.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Complex Plane
The complex plane is much like a two-dimensional cartesian plane. However, it has a unique twist. Instead of traditional x and y axes, it uses the real and imaginary numbers. Each point in this plane represents a complex number expressed as \(z = x + yi\). Here, \(x\) is the real part, and \(y\) is the imaginary part.
- The horizontal axis is the real axis.
- The vertical axis is the imaginary axis.
Transformation
Transformation in mathematics involves changing a shape or a position. In the complex plane, transformations apply to complex numbers. They change how these numbers are plotted.
The particular transformation in our case is achieved through the function \(w = z^2\). This means we square the complex number \(z = x + yi\), resulting in \(w = x^2 - y^2 + 2xyi\). What does this do?
The particular transformation in our case is achieved through the function \(w = z^2\). This means we square the complex number \(z = x + yi\), resulting in \(w = x^2 - y^2 + 2xyi\). What does this do?
- Real Part: From \(x^2 - y^2\), showing horizontal movement.
- Imaginary Part: From \(2xy\), showing vertical movement.
Imaginary Axis
The imaginary axis is like the y-axis on a standard coordinate plane. It represents all numbers with no real parts, only imaginary.
In our exercise, after applying the transformation, the output \(w = 2x^2i\) lands entirely on the imaginary axis. The absence of a real part (where \(u = 0\) in \(w = u + vi\)) confirms this.
In our exercise, after applying the transformation, the output \(w = 2x^2i\) lands entirely on the imaginary axis. The absence of a real part (where \(u = 0\) in \(w = u + vi\)) confirms this.
- The numbers \(w\) plotted here follow the form \(vi\).
- In our case, each \(w\) looks like \(2x^2i\). This means the transformation gives a purely imaginary result.
Parabola
A parabola is a curve where each point is at an equal distance from a fixed point (the focus) and a line (the directrix). In our context, it emerges when we map points through the transformation.
Upon applying \(w = z^2\) to the line \(y = x\), we get results that resemble a parabola in form. Here the vertices touch the imaginary axis:
Upon applying \(w = z^2\) to the line \(y = x\), we get results that resemble a parabola in form. Here the vertices touch the imaginary axis:
- The transformation outputs \(w = 2x^2i\).
- The imaginary part of \(w\) is proportional to \(x^2\), which is quadratic.