Math Problem Statement

Find the image of the following under the map W = 1/2: (a) |z + 1| = 1, (b) |z - 2i| = 2, (c) x = 1, (d) 1 < x < 2, (e) x = 2, (f) |z - 1| = 1.

Solution

The problem involves determining the image of various sets under the map W=12W = \frac{1}{2}, which is a transformation on the complex plane. We will proceed with each subquestion and compute the corresponding images under this map.

General Approach: The map W=12W = \frac{1}{2} means we are transforming the complex number zz into a new number, which is always half of the original value of zz. Hence, if zz is mapped to W=12W = \frac{1}{2}, the image of any point or set depends on how this transformation affects the geometric properties of that set.

Let me now analyze each part of the question:

(a) z+1=1|z + 1| = 1

This describes a circle centered at z=1z = -1 with radius 1. Under the map, each point on this circle is mapped to W=12(z)W = \frac{1}{2}(z). The image will also be a circle, but with a new center and radius scaled by 12\frac{1}{2}. The new circle will have center W=12(1)=12W = \frac{1}{2}(-1) = -\frac{1}{2}, and radius 12(1)=12\frac{1}{2}(1) = \frac{1}{2}.

(b) z2i=2|z - 2i| = 2

This describes a circle centered at z=2iz = 2i with radius 2. After applying the map, the new center is W=12(2i)=iW = \frac{1}{2}(2i) = i, and the new radius is 12(2)=1\frac{1}{2}(2) = 1. Thus, the image is a circle with center ii and radius 1.

(c) x=1x = 1

This represents the vertical line in the complex plane where the real part of zz is 1. The transformation scales the real part of zz by 12\frac{1}{2}. Hence, the image will be the line where the real part of WW is 12\frac{1}{2}, i.e., the line x=12x = \frac{1}{2}.

(d) 1<x<21 < x < 2

This describes a vertical strip where the real part of zz lies between 1 and 2. Under the map, the real part of zz is halved, so the image is a strip where 12<x<1\frac{1}{2} < x < 1.

(e) x=2x = 2

This is a vertical line where the real part of zz is 2. After applying the map, the real part of WW becomes 12(2)=1\frac{1}{2}(2) = 1, so the image is the line x=1x = 1.

(f) z1=1|z - 1| = 1

This describes a circle centered at z=1z = 1 with radius 1. After the transformation, the center becomes W=12(1)=12W = \frac{1}{2}(1) = \frac{1}{2}, and the radius becomes 12(1)=12\frac{1}{2}(1) = \frac{1}{2}. Hence, the image is a circle centered at 12\frac{1}{2} with radius 12\frac{1}{2}.


Would you like more details on any of these transformations or additional explanations for the geometric reasoning?

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Math Problem Analysis

Mathematical Concepts

Complex Plane
Geometric Transformations
Circle Mapping
Linear Transformation

Formulas

W = 1/2

Theorems

Mapping Transformation
Geometric Properties of Complex Numbers

Suitable Grade Level

Grades 11-12