Chapter 3: Problem 44
Let \(T\) be a linear transformation from \(\mathbb{R}^{2}\) to \(\mathbb{R}^{2}\) (or from \(\mathbb{R}^{3}\) to \(\mathbb{R}^{3}\) ). Prove that \(T\) maps a straight line to a straight line or a point. [Hint: Use the vector form of the equation of a line.]
Short Answer
Expert verified
A linear transformation maps a line to either another line or a single point.
Step by step solution
01
Understand the Problem
The problem asks us to prove that a linear transformation \(T\) from \(\mathbb{R}^2\) or \(\mathbb{R}^3\) maps a straight line to either another straight line or a point. We will use the vector form of the equation of a line, \(\mathbf{r}(t) = \mathbf{a} + t\mathbf{b}\), to show this.
02
Consider the Vector Form of a Line
A line in \(\mathbb{R}^2\) or \(\mathbb{R}^3\) can be described by the vector equation \(\mathbf{r}(t) = \mathbf{a} + t\mathbf{b}\), where \(\mathbf{a}\) is a fixed point on the line, \(\mathbf{b}\) is a direction vector, and \(t\) is a scalar parameter.
03
Apply Transformation to the Line Equation
Apply the linear transformation \(T\) to the vector form of the line: \(T(\mathbf{r}(t)) = T(\mathbf{a} + t\mathbf{b}) = T(\mathbf{a}) + T(t\mathbf{b})\).
04
Use Property of Linear Transformations
A key property of linear transformations is that \(T(t\mathbf{b}) = tT(\mathbf{b})\) for any scalar \(t\). Therefore, \(T(\mathbf{r}(t)) = T(\mathbf{a}) + tT(\mathbf{b})\). This expression is still in the form of a line, \(\mathbf{c} + t\mathbf{d}\), where \(\mathbf{c} = T(\mathbf{a})\) and \(\mathbf{d} = T(\mathbf{b})\).
05
Consider Special Case of a Point
If the direction vector \(\mathbf{b}\) is transformed such that \(T(\mathbf{b}) = \mathbf{0}\), then the transformation maps every point on the line to the fixed point \(T(\mathbf{a})\). Therefore, all points map to a single point.
06
Conclude the Argument
Since the transformation \(T\) maps the original line \(\mathbf{r}(t) = \mathbf{a} + t\mathbf{b}\) to \(T(\mathbf{a}) + tT(\mathbf{b})\), which is either another line (if \(T(\mathbf{b}) eq \mathbf{0}\)) or a point (if \(T(\mathbf{b}) = \mathbf{0}\)), we have shown that \(T\) maps a line to a line or a point.
Unlock Step-by-Step Solutions & Ace Your Exams!
-
Full Textbook Solutions
Get detailed explanations and key concepts
-
Unlimited Al creation
Al flashcards, explanations, exams and more...
-
Ads-free access
To over 500 millions flashcards
-
Money-back guarantee
We refund you if you fail your exam.
Over 30 million students worldwide already upgrade their learning with 91Ó°ÊÓ!
Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Line Mapping
In mathematics, line mapping is a way to transform a line from one space to another using a function or transformation. Specifically, when dealing with linear transformations such as those denoted by \(T\), we are interested in how these transformations affect geometric figures like lines. A linear transformation is a special kind of function that maintains the operations of addition and scalar multiplication. This means when you apply a linear transformation to a line, it will always result in another line or a point.
Key ideas related to line mapping through linear transformations include:
Key ideas related to line mapping through linear transformations include:
- A line in \(\mathbb{R}^2\) or \(\mathbb{R}^3\) is converted via the transformation \(T\) into a line or a single point.
- The properties of linear transformations that ensure the line remains a line (or a point) include linearity; that is, transformations are consistent and predictable for vectors.
- This understanding is pivotal in fields like computer graphics, where transformations (like rotations and translations) must maintain the structural integrity of geometric shapes.
Vector Form of a Line
The vector form of a line is a powerful tool to describe lines in space. It is expressed as \(\mathbf{r}(t) = \mathbf{a} + t\mathbf{b}\), where:
In the context of transformations, applying a transformation \(T\) to a line in vector form means transforming each component: the fixed point \(\mathbf{a}\) and the direction vector \(\mathbf{b}\). This results in a new line or a singular point, leveraging the properties of linearity in the transformation to directly predict the outcome.
This linearity assures that the vector form remains valid post-transformation, making it an essential concept in linear algebra and its applications.
- \(\mathbf{a}\) is a position vector pointing to a specific point on the line.
- \(\mathbf{b}\) is the direction vector, showing the direction in which the line extends.
- \(t\) is a scalar, allowing you to travel along the line by scaling the direction vector.
In the context of transformations, applying a transformation \(T\) to a line in vector form means transforming each component: the fixed point \(\mathbf{a}\) and the direction vector \(\mathbf{b}\). This results in a new line or a singular point, leveraging the properties of linearity in the transformation to directly predict the outcome.
This linearity assures that the vector form remains valid post-transformation, making it an essential concept in linear algebra and its applications.
Transformation Properties
Transformation properties refer to the characteristics that define and dictate how transformations like linear transformations behave. For a transformation \(T\) to be linear, it has to satisfy two primary properties:
If the transformation results in \(T(\mathbf{b}) = \mathbf{0}\), every point on the line is mapped to \(T(\mathbf{a})\), effectively resulting in a single point. Understanding these properties allows one to fully comprehend the impact of linear transformations on lines and other geometric structures, which is a crucial aspect of numerous scientific and engineering domains.
- Additivity: For vectors \(\mathbf{u}\) and \(\mathbf{v}\), \(T(\mathbf{u} + \mathbf{v}) = T(\mathbf{u}) + T(\mathbf{v})\).
- Homogeneity: For any vector \(\mathbf{v}\) and scalar \(c\), \(T(c\mathbf{v}) = cT(\mathbf{v})\).
If the transformation results in \(T(\mathbf{b}) = \mathbf{0}\), every point on the line is mapped to \(T(\mathbf{a})\), effectively resulting in a single point. Understanding these properties allows one to fully comprehend the impact of linear transformations on lines and other geometric structures, which is a crucial aspect of numerous scientific and engineering domains.