Linear Transformations using polynomials

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Homework Help Overview

The discussion revolves around linear transformations in the context of polynomials, specifically focusing on the space of polynomials of degree at most 3, denoted as P3. The linear transformation D is defined as the derivative of a polynomial, and participants are tasked with finding the matrix representation of this transformation with respect to the standard basis and explaining a property of the matrix raised to the fourth power.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss how to derive the matrix representation of the transformation by considering the effect of D on the basis elements of P3. There are attempts to articulate the reasoning behind why raising the matrix to the fourth power results in a zero matrix, with some participants expressing difficulty in verbalizing their thoughts.

Discussion Status

Some guidance has been offered regarding the approach to finding the matrix representation, including hints about considering the derivatives of the basis elements. However, there is still uncertainty among participants about explaining the property of the matrix when raised to the fourth power, indicating an ongoing exploration of the concepts involved.

Contextual Notes

Participants express constraints in articulating their understanding of the relationship between differentiation and the degree of polynomials, which is central to the discussion of the transformation's properties.

mbud
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Homework Statement



Let P3 be the space of all polynomials (with real coefficients) of degree at most 3. Let
D : P3 -> P3 be the linear transformation given by taking the derivative of a polynomial.
That is
D(a + bx + cx2 + dx3) = b + 2cx + 3dx2:
Let B be the standard basis {1; x; x2; x3} of P3.
(a) Find the matrix MD of D with respect to the standard basis.
(b) Explain, without doing any matrix calculations, why (MD)4 = 0.

Homework Equations





The Attempt at a Solution


i know it may be a simple question but i don't even know where to begin
but in a attempt is
MD = [1 1 1 1;
0 2 3 0]
 
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Welcome to PF!

Hi mbud! Welcome to PF! :smile:

(try using the X2 tag just above the Reply box :wink:)
mbud said:
Let P3 be the space of all polynomials (with real coefficients) of degree at most 3. Let
D : P3 -> P3 be the linear transformation given by taking the derivative of a polynomial.
That is
D(a + bx + cx2 + dx3) = b + 2cx + 3dx2:
Let B be the standard basis {1; x; x2; x3} of P3.
(a) Find the matrix MD of D with respect to the standard basis.
(b) Explain, without doing any matrix calculations, why (MD)4 = 0.

To find M, you only need the effect of M on the four basis elements. Sooo …

Hint: what is x2 as a vector? what is Dx2 as a vector? :wink:
 
More specifically, since the standard basis is 1, x, x2, and x3, take the derivative of each and write it in terms of those. The coefficients give each column of the matrix.
 
Thanks, for the help, but i still don't know how to explain (MD)^4 = 0
I can show it using matrices, but when it comes to words, I am flabbergasted.
 
mbud said:
Thanks, for the help, but i still don't know how to explain (MD)^4 = 0
I can show it using matrices, but when it comes to words, I am flabbergasted.

Hint: if V is the vector form of a polynomial ax3 + bx2 + cx + d, what is (MD)4V the vector of? :wink:
 
Differentiation does what to the degree of a polynomial? This is nothing to do with vectors, or vector spaces, or matrices - sometimes you just have to look at things and think for a little bit.
 

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