Chapter 6: Problem 35
Find the dimension of the vector space \(V\) and give a basis for \(V\). $$V=\left\\{p(x) \text { in } \mathscr{P}_{2}: p(1)=0\right\\}$$
Short Answer
Expert verified
The dimension of \( V \) is 2, with the basis \( \{ x^2 - 1, x - 1 \} \).
Step by step solution
01
Understand the Vector Space
The vector space \( V \) consists of all polynomials in \( \mathscr{P}_2 \), which means polynomials of degree at most 2, with the condition that \( p(1) = 0 \). This condition will restrict the polynomials in the space.
02
General Form of Polynomials in \( \mathscr{P}_2 \)
The general form of a polynomial in \( \mathscr{P}_2 \) is \( p(x) = ax^2 + bx + c \). Since \( p(1) = 0 \), substituting 1 for \( x \) gives \( a(1)^2 + b(1) + c = 0 \), simplifying to \( a + b + c = 0 \).
03
Derive Basis for \( V \)
The condition \( a + b + c = 0 \) allows us to express one coefficient in terms of the others, for instance, \( c = -a - b \). Therefore, a polynomial in \( V \) can be rewritten as \( p(x) = ax^2 + bx - a - b \), which simplifies to \( a(x^2 - 1) + b(x - 1) \). The polynomials \( x^2 - 1 \) and \( x - 1 \) are linearly independent and span \( V \).
04
Identify and Verify Basis
The set \( \{ x^2 - 1, x - 1 \} \) is a basis for \( V \), as these polynomials are linearly independent and satisfy the condition \( p(1) = 0 \). The dimension of \( V \) is the number of vectors in this basis, which is 2.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Polynomial Vector Space
A polynomial vector space is a collection of polynomials that follow specific properties, functioning similarly to vectors in traditional vector spaces. The set of polynomials in a polynomial vector space can vary based on the conditions defining the space. In our exercise, the vector space \( V \) contains polynomials from \( \mathscr{P}_2 \). This indicates polynomials with a degree of at most 2. Each polynomial is of the form \( p(x) = ax^2 + bx + c \). However, a condition is given that \( p(1) = 0 \), which restricts \( V \) such that any polynomial within the space must satisfy this condition.This condition implies that the sum of the coefficients (replacing \( x \) with 1) follows \( a + b + c = 0 \). Consequently, the polynomials are fully characterized by two parameters (since one can be expressed in terms of the others), slightly similar to vectors in a geometric plane.
Basis of a Vector Space
A basis of a vector space is a collection of vectors that are both linearly independent and span the entire space. These vectors form a kind of 'skeleton' for the vector space. Each polynomial in the vector space can be expressed uniquely as a linear combination of the basis vectors.In the context of polynomial vector spaces, the basis must satisfy any given conditions of the space. For \( V \), the vectors \( \{x^2 - 1, x - 1\} \) were found by rewriting the polynomial after applying the given condition \( a + b + c = 0 \). Expressing this gives us \( p(x) = a(x^2 - 1) + b(x - 1) \).The polynomials \( x^2 - 1 \) and \( x - 1 \) are confirmed as linearly independent because there are no scalar multiples (other than zeros) where one can be written as a linear combination of the other. Therefore, these polynomials form a valid basis for \( V \).
Dimension of a Vector Space
The dimension of a vector space is defined as the number of vectors in its basis. It gives a measure of the "size" or "capacity" of the space in terms of how many directions it can extend.In our problem, the dimension of the vector space \( V \) is determined by the number of polynomials in the basis \( \{x^2 - 1, x - 1\} \). Since there are two polynomials in this basis, the dimension of \( V \) is 2.This tells us that even with the restriction \( p(1) = 0 \), the space maintains two independent "dimensions" or degrees of freedom, meaning it spans a plane-like structure in the space of degree-2 polynomials. Knowing the dimension is crucial as it directly relates to how the space can be manipulated and the types of transformations it supports.