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Let \(T : \mathbb{P}_{2} \rightarrow \mathbb{P}_{4}\) be the transformation that maps a polynomial \(\mathbf{p}(t)\) into the polynomial \(\mathbf{p}(t)+t^{2} \mathbf{p}(t)\) a. Find the image of \(\mathbf{p}(t)=2-t+t^{2}\) b. Show that \(T\) is a linear transformation. c. Find the matrix for \(T\) relative to the bases \(\left\\{1, t, t^{2}\right\\}\) and \(\left\\{1, t, t^{2}, t^{3}, t^{4}\right\\}\)

Short Answer

Expert verified
a. Image: \( 2 - t + 3t^2 - t^3 + t^4 \). b. Yes, \( T \) is linear. c. Matrix: \( \begin{bmatrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 1 & 0 & 1 \\ 0 & 1 & 0 \\ 0 & 0 & 1 \end{bmatrix} \).

Step by step solution

01

Calculate the Image of \( \mathbf{p}(t) = 2 - t + t^2 \)

The image of a polynomial \( \mathbf{p}(t) \) under the transformation \( T \) is given by \( T(\mathbf{p}(t)) = \mathbf{p}(t) + t^2 \mathbf{p}(t) \). Compute \( t^2 \mathbf{p}(t) \) first:\[t^2 \mathbf{p}(t) = t^2 (2 - t + t^2) = 2t^2 - t^3 + t^4.\]Now, add \( \mathbf{p}(t) \) and \( t^2 \mathbf{p}(t) \):\[T(\mathbf{p}(t)) = (2 - t + t^2) + (2t^2 - t^3 + t^4) = 2 - t + 3t^2 - t^3 + t^4.\]
02

Verify Linearity of Transformation \( T \)

To prove that \( T \) is linear, we need to show that for any polynomials \( \mathbf{p}(t) \) and \( \mathbf{q}(t) \) in \( \mathbb{P}_2 \) and any scalar \( c \), the transformation satisfies:1. \( T(\mathbf{p}(t) + \mathbf{q}(t)) = T(\mathbf{p}(t)) + T(\mathbf{q}(t)) \)2. \( T(c \cdot \mathbf{p}(t)) = c \cdot T(\mathbf{p}(t)) \)**Proof For 1:**\[T(\mathbf{p}(t) + \mathbf{q}(t)) = (\mathbf{p}(t) + \mathbf{q}(t)) + t^2(\mathbf{p}(t) + \mathbf{q}(t)) = \mathbf{p}(t) + t^2 \mathbf{p}(t) + \mathbf{q}(t) + t^2 \mathbf{q}(t) = T(\mathbf{p}(t)) + T(\mathbf{q}(t))\]**Proof For 2:**\[T(c \cdot \mathbf{p}(t)) = (c \cdot \mathbf{p}(t)) + t^2(c \cdot \mathbf{p}(t)) = c \cdot (\mathbf{p}(t) + t^2 \mathbf{p}(t)) = c \cdot T(\mathbf{p}(t))\]Therefore, \( T \) is linear.
03

Determine Matrix of \( T \) Relative to Given Bases

To express \( T \) as a matrix with respect to the basis \( \{1, t, t^2\} \) for \( \mathbb{P}_2 \) and basis \( \{1, t, t^2, t^3, t^4\} \) for \( \mathbb{P}_4 \), we first calculate \( T \) for each basis polynomial of \( \mathbb{P}_2 \):1. \( T(1) = 1 + t^2 \times 1 = 1 + t^2 \).2. \( T(t) = t + t^2t = t + t^3 \).3. \( T(t^2) = t^2 + t^2 \cdot t^2 = t^2 + t^4 \).These correspond to the following vectors in \( \mathbb{P}_4 \):- \( T(1) = [1, 0, 1, 0, 0] \)- \( T(t) = [0, 1, 0, 1, 0] \)- \( T(t^2) = [0, 0, 1, 0, 1] \)Thus, the matrix \( A \) representing \( T \) is:\[A = \begin{bmatrix} 1 & 0 & 0 \ 0 & 1 & 0 \ 1 & 0 & 1 \ 0 & 1 & 0 \ 0 & 0 & 1 \end{bmatrix}\]

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Polynomial Transformation
A polynomial transformation is a type of function where a given polynomial is transformed or altered to form another polynomial. In this context, we have a transformation, denoted as \( T \), which acts on a polynomial \( \mathbf{p}(t) \) to create a new polynomial of a higher degree. The primary operation here involves combining the polynomial \( \mathbf{p}(t) \) with its product with \( t^2 \), as described by the transformation \( T(\mathbf{p}(t)) = \mathbf{p}(t) + t^2 \mathbf{p}(t) \). This effectively changes both the coefficients and the degree of the initial polynomial.
Such transformations are crucial in mathematics because they allow us to explore how polynomials evolve under specific operations, potentially leading to insights in fields like algebraic geometry or solving polynomial equations. In our specific exercise, by transforming \( \mathbf{p}(t) = 2-t+t^2 \), we see how the polynomial's terms adjust
  • The constant term stays the same.
  • The linear term remains unchanged in the transformed polynomial.
  • The quadratic term triples its coefficient.
  • New cubic and quartic terms appear.
Understanding polynomial transformations helps us explore mathematical concepts systematically and understand the manipulation of polynomial degrees.
Matrix Representation of Linear Maps
To represent a linear transformation through a matrix form, we first need to consider the basis of the vector spaces involved. Any linear transformation can be represented in a matrix form when we select bases for both the domain and the codomain.
In our problem, transformation \( T: \mathbb{P}_2 \rightarrow \mathbb{P}_4 \) is represented relative to specific polynomial bases:
  • Basis for \( \mathbb{P}_2 \): \( \{1, t, t^2\} \)
  • Basis for \( \mathbb{P}_4 \): \( \{1, t, t^2, t^3, t^4\} \)
The matrix of \( T \) is constructed by determining the image of each basis polynomial from \( \mathbb{P}_2 \) and expressing these images as vectors relative to the \( \mathbb{P}_4 \) basis. The transformation \( T \) applied to these basis polynomials delivers new polynomials, each represented as a column in the matrix. The final matrix offers a structured way to compute how any polynomial in the initial basis will transform into the codomain’s basis.
Matrix representation is a powerful tool in linear algebra, allowing for extensive operations like transformations, duplications, and more, by simplifying the otherwise complex polynomial operations into easy matrix calculations.
Basis and Coordinate Systems
The concept of basis and coordinate systems is fundamental to understanding spaces and transformations between them in linear algebra. A basis of a vector space is a set of vectors that are linearly independent and span the entire space, allowing every element in the space to be expressed as a linear combination of these basis vectors. In our exercise, two different polynomial spaces have different bases:
  • For \( \mathbb{P}_2 \), the basis is \( \{1, t, t^2\} \), crucial for expressing quadratic polynomials.
  • For \( \mathbb{P}_4 \), the basis is \( \{1, t, t^2, t^3, t^4\} \), suitable for fourth-degree polynomials.
By understanding the basis, we know that a polynomial transformation \( T \) can be represented in a structured manner, and any polynomial can be uniquely decomposed into its basis components. This decomposition allows for transformations like \( T \) to apply linear operations systematically.
Providing a coordinate system through a chosen basis simplifies complex algebraic operations and enables the transformations to be studied through geometric intuition. Thus, the basis plays a pivotal role in interpreting transformations across different dimensions, making complex relationships comprehensible and easier to manipulate.

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Most popular questions from this chapter

In Exercises 21 and \(22, A\) and \(B\) are \(n \times n\) matrices. Mark each statement True or False. Justify each answer. a. If \(A\) is \(3 \times 3,\) with columns \(\mathbf{a}_{1}, \mathbf{a}_{2},\) and \(\mathbf{a}_{3},\) then \(\operatorname{det} A\) equals the volume of the parallelepiped determined by \(\mathbf{a}_{1},\) \(\mathbf{a}_{2}\) and \(\mathbf{a}_{3}\) . b. \(\operatorname{det} A^{T}=(-1)\) det \(A\) c. The multiplicity of a root \(r\) of the characteristic equation of \(A\) is called the algebraic multiplicity of \(r\) as an eigen-value of \(A .\) d. A row replacement operation on \(A\) does not change the eigenvalues.

In Exercises \(3-6,\) solve the initial value problem \(\mathbf{x}^{\prime}(t)=A \mathbf{x}(t)\) for \(t \geq 0,\) with \(\mathbf{x}(0)=(3,2) .\) Classify the nature of the origin as an attractor, repeller, or saddle point of the dynamical system described by \(\mathbf{x}^{\prime}=A \mathbf{x}\) . Find the directions of greatest attraction and/or repulsion. When the origin is a saddle point, sketch typical traiectories. $$ A=\left[\begin{array}{ll}{1} & {-2} \\ {3} & {-4}\end{array}\right] $$

In Exercises \(13-16,\) define \(T : \mathbb{R}^{2} \rightarrow \mathbb{R}^{2}\) by \(T(\mathbf{x})=A \mathbf{x}\) . Find a basis \(\mathcal{B}\) for \(\mathbb{R}^{2}\) with the property that \([T]_{\mathcal{B}}\) is diagonal. $$ A=\left[\begin{array}{rr}{5} & {-3} \\ {-7} & {1}\end{array}\right] $$

In Exercises \(3-6,\) solve the initial value problem \(\mathbf{x}^{\prime}(t)=A \mathbf{x}(t)\) for \(t \geq 0,\) with \(\mathbf{x}(0)=(3,2) .\) Classify the nature of the origin as an attractor, repeller, or saddle point of the dynamical system described by \(\mathbf{x}^{\prime}=A \mathbf{x}\) . Find the directions of greatest attraction and/or repulsion. When the origin is a saddle point, sketch typical traiectories. $$ A=\left[\begin{array}{rr}{-2} & {-5} \\ {1} & {4}\end{array}\right] $$

Use a property of determinants to show that \(A\) and \(A^{T}\) have the same characteristic polynomial.

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