Need some hints on my HW about Linear functionals

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SUMMARY

This discussion focuses on understanding linear functionals, specifically the properties and definitions associated with them. The participant highlights confusion regarding the notation and the mapping of polynomials, particularly in the context of the linear functional $$\varphi(P)$$, which is defined as $$\varphi(P) = {a}_{0}p(0) + \sum_{k=1}^{m} {p}^{(k)}(0)$$. Key concepts include the polynomial space $$P_m(\mathbb{F})$$ and the importance of consistent notation in mathematical expressions. The participant seeks clarity on the implications of these definitions and how they relate to their homework questions.

PREREQUISITES
  • Understanding of linear functionals and their properties
  • Familiarity with polynomial spaces, specifically $$P_m(\mathbb{F})$$
  • Knowledge of derivatives and their notation, particularly $$p^{(k)}(x)$$
  • Basic proficiency in LaTeX for mathematical typesetting
NEXT STEPS
  • Research the properties of linear functionals in functional analysis
  • Study the structure and properties of polynomial spaces, focusing on $$P_m(\mathbb{F})$$
  • Learn about the implications of notation consistency in mathematical proofs
  • Explore the concept of extending bases in vector spaces
USEFUL FOR

Students studying linear algebra, particularly those working with linear functionals and polynomial spaces, as well as educators seeking to clarify notation and concepts in mathematical communication.

BaconInDistress
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I not very good at using the LaTex editor, so I took a photo of my HW questions.
View attachment 8831
For the first question, I'm not really sure how to get started, should I write out a specific case? Like what would $$\varphi (P)$$ be when m=1?

For the second question, I know that a linear functional have two properties, one being $$\varphi(u +v) = \varphi(u) + \varphi(v)$$ and the other one being $$\varphi(\lambda u) = \lambda\varphi(u)$$. I'm a bit confused about the mapping, is it saying that when we have a polynomial P(z), the map makes it goes to p(0) for all z?
 

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Perhaps you should start by defining notations, including $\mathbb{F}$, $P_m(\mathbb{F})$ and $p^{(k)}(x)$. Also, it is not very clear which of $p$'s are uppercase and which are lowercase letters. For example, in problem 1 in the left-hand side $\varphi(P)$ the letter $P$ seems to be uppercase, but in the right-hand side it is probably lowercase.
 
According to the textbook we use, $$F$$ is a field over $$\Bbb{R}$$ or $$\Bbb{C}$$. $${P}_{m}(F)$$ is the polynomial space of degree m.
One of the many problem with my homework is indeed the handwriting, my professor is not very consistent with his upper and lower case letters. I just copied down what he wrote.
I think for question one, we need to prove the existence of constants $${a}_{0},...,{a}_{m}$$ such that the linear functional $$\varphi (P) = {a}_{0}p(0) + \sum_{k=1}^{m} {p}^{(k)}(0)$$
Not really sure how to go from there
 
BaconInDistress said:
According to the textbook we use, $$F$$ is a field over $$\Bbb{R}$$ or $$\Bbb{C}$$.
"A field over $\mathbb{R}$" sounds strange. There are vector spaces and algebras over fields. Perhaps $\mathbb{F}$ is simply a field.

BaconInDistress said:
I think for question one, we need to prove the existence of constants $${a}_{0},...,{a}_{m}$$ such that the linear functional $$\varphi (P) = {a}_{0}p(0) + \sum_{k=1}^{m} {p}^{(k)}(0)$$
Not really sure how to go from there
I think $p$ should be lowercase in the left-hand side as well.

Every functional on $\mathbb{F}^m$ has the form $\varphi((b_0,\ldots,b_m))=a_0b_0+\dots a_mb_m$ for some constants $a_0,\ldots,a_m$. Now suppose $p(t)=b_0+b_1x+\dots b_mx^m$. What are $p(0), p'(0), \ldots, p^{(m)}(0)$?

I'm a bit confused about the mapping, is it saying that when we have a polynomial P(z), the map makes it goes to p(0) for all z?
Yes, I believe the function maps a polynomial $p(z)$ to $(p(0))^2$. The question is whether it is a linear functional.

In problem 3, what is the third derivative of a polynomial whose degree is at most 2?

For problem 4, extend $v$ to a basis of the space $V$.
 

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