Chapter 20: Problem 3
A curve in the \(z\) -plane and a complex mapping \(w=f(z)\) are given. In each case, find the image curve in the \(w\) -plane. Hyperbola \(x y=1\) under \(w=z^{2}\)
Short Answer
Expert verified
The image is a horizontal line at \(v = 2\) in the \(w\)-plane.
Step by step solution
01
Understanding the Given Curve
The given curve is a hyperbola in the complex plane, expressed as the equation \(xy = 1\). Here, \(x\) and \(y\) are the real and imaginary parts of the complex number \(z = x + yi\). This means any point \(z\) on the curve satisfies \(xy = 1\).
02
Identifying the Mapping Function
The mapping function is given as \(w = z^2\). This means that every point \(z = x + yi\) in the \(z\)-plane is transformed to a new point \(w\) in the \(w\)-plane, where \(w = (x + yi)^2 = x^2 - y^2 + 2xyi\).
03
Calculating the Image in the w-plane
We start by substituting the condition \(xy = 1\) into our mapping \(w = x^2 - y^2 + 2xyi\). The imaginary part \(2xy = 2 \cdot 1 = 2\) because \(xy = 1\). So the imaginary part of \(w\) is always 2 for any \(z\) on the hyperbola. The real part is \(x^2 - y^2\), which varies based on \(x\) and \(y\).
04
Conclusion about the Image Curve
The image of the hyperbola \(xy = 1\) under the mapping \(w = z^2\) is a set of points \(w = u + vi\) where \(v = 2\), making it a horizontal line in the \(w\)-plane. The real component \(u = x^2 - y^2\), can take any real value, so the line is infinite in the horizontal direction.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Complex Mapping
In complex analysis, a complex mapping refers to the transformation of complex numbers from one plane to another, typically using a function. Imagine you have a point on the complex plane, often called the \(z\)-plane. Through a complex mapping function, like \(w=f(z)\), this point is transformed or mapped to another point on a different plane, the \(w\)-plane.
- The \(z\)-plane is where the original complex number \(z\) resides, expressed as \(z = x + yi\).
- The \(w\)-plane is where the image, or transformed point \(w\), is plotted.
Hyperbola
A hyperbola is a type of conic section, which is a curve generated by intersecting a cone with a plane. In a Cartesian coordinate system, a hyperbola can be represented by equations like \(xy=1\). It consists of two separate curves that mirror each other.
- Unlike an ellipse or circle, a hyperbola opens outward.
- Each of the 'branches' of a hyperbola approaches two fixed lines, called asymptotes, but never intersects them.
Complex Plane
The complex plane is a two-dimensional plane facilitating the visualization of complex numbers. It is akin to a Cartesian coordinate system but designed specifically for the complex number system. Here, a complex number \(z = x + yi\) has:
- The real part \(x\) as its horizontal coordinate,
- The imaginary part \(y\) as its vertical coordinate.
Image Curve
An image curve refers to the resultant curve after a complex mapping transformation is applied to an original curve. In the context of our exercise, the original curve given by the hyperbola \(xy=1\) is transformed through the mapping \(w=z^2\).
- By substituting \(xy=1\) into this function, we derive the new image in the \(w\)-plane.
- The result is a line rather than a typical hyperbolic shape.