Chapter 28: Problem 2
If \(\mathrm{a}=(1,2,3,4)\) and \(\mathbf{b}=(4,3,2,1)\), explain why \(\\{\mathrm{a}, \mathbf{b}\\}\) may be extended to a basis of \(\mathbb{R}^{4}\). Then find a basis of \(\mathbb{R}^{4}\) which includes a and \(\mathbf{b}\).
Short Answer
Expert verified
\(\{\mathbf{a}, \mathbf{b}, (1,0,0,0), (0,1,0,0)\}\) can be a basis of \(\mathbb{R}^4\).
Step by step solution
01
Understand the Dimensions
We're working in \(\mathbb{R}^4\), which means any basis here must have 4 linearly independent vectors. The vectors \(\mathbf{a}\) and \(\mathbf{b}\) are given as two vectors in \(\mathbb{R}^4\).
02
Check Linear Independence
We need to verify if \(\mathbf{a}\) and \(\mathbf{b}\) are linearly independent. We check if their linear combination gives the zero vector only when both coefficients are zero. Set \(c_1(1,2,3,4) + c_2(4,3,2,1) = (0,0,0,0)\). Solving these equations, we find that \(c_1 = c_2 = 0\) is the only solution, proving they are linearly independent.
03
Number of Vectors in the Span
Since \(\mathbf{a}\) and \(\mathbf{b}\) are linearly independent, they span a 2-dimensional subspace of \(\mathbb{R}^4\). To form a basis of \(\mathbb{R}^4\), we need 2 more vectors.
04
Complete the Basis
To extend \(\{\mathbf{a}, \mathbf{b}\}\) to a basis of \(\mathbb{R}^4\), add two more vectors. Choose canonical basis vectors in \(\mathbb{R}^4\) like \(\mathbf{c} = (1,0,0,0)\) and \(\mathbf{d} = (0,1,0,0)\). Now, \(\{\mathbf{a}, \mathbf{b}, \mathbf{c}, \mathbf{d}\}\) forms a basis, as they are linearly independent and span the 4-dimensional space.
05
Verify the Basis
Check linear independence of \(\{\mathbf{a}, \mathbf{b}, \mathbf{c}, \mathbf{d}\}\). Form a matrix \(A\) with these vectors as rows and perform row-reduction. Since all rows are pivot rows, the matrix has rank 4, confirming linear independence and basis status.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Basis of Vector Space
A basis of a vector space is a fundamental concept in linear algebra. It is essentially a set of vectors that is both linearly independent and spans the entire space. This means that any vector in the space can be expressed as a linear combination of the basis vectors. In the context of \(\mathbb{R}^{4}\), the requirement for a set of vectors like \(\{\mathbf{a}, \mathbf{b}\}\) to be extended to form a basis is that they must be part of a set of four linearly independent vectors. Once they fulfill this requirement, they form what's known as a basis, providing a framework that describes the entire four-dimensional space. Understanding what constitutes a basis helps in solving vector space problems, such as determining how many vectors are needed and verifying their independence.
Linear Independence
Linear independence is an important quality for a set of vectors. If vectors are linearly independent, it means no vector in the set can be written as a combination of the others. To verify the linear independence of given vectors like \(\mathbf{a} = (1,2,3,4)\) and \(\mathbf{b} = (4,3,2,1)\), we set them in an equation: \[c_1\mathbf{a} + c_2\mathbf{b} = (0,0,0,0)\]. Solving this equation, if the only solution is \(c_1 = 0\) and \(c_2 = 0\), the vectors are confirmed to be linearly independent.This concept is crucial because, without linear independence, a complete and non-redundant basis for vector space cannot be formed.
Dimension of a Vector Space
The dimension of a vector space is defined as the number of vectors in a basis for the space. For \(\mathbb{R}^4\), this dimension is 4 because it is a four-dimensional space.In simpler terms, the dimension tells us how many directions or degrees of freedom the vector space has. Each vector in a basis represents one of these directions.The concept of dimension is essential for understanding how big or complex a vector space is and how many vectors are required to describe it completely.
Row Reduction
Row reduction is a method used in linear algebra to simplify matrices. It involves performing a series of operations to transform a matrix into a simpler form, usually the row-echelon form or the reduced row-echelon form.
This technique is often used to determine the rank of a matrix, check linear independence, and solve systems of linear equations. In the context of creating a basis, row reduction helps verify that a chosen set of vectors, arranged as rows of a matrix, are independent.
Through row reduction, you can confirm the presence of pivot positions in each row, indicating the vectors span the entire space and can serve as a basis.
Vector Space
A vector space is a collection of vectors that can be added together and multiplied by scalars. It is defined by a set of vectors that satisfy certain axioms, such as closure under addition and scalar multiplication.Vector spaces are not restricted to just \(\mathbb{R}^4\), but can exist in any dimension. In \(\mathbb{R}^4\), the vector space comprises all possible 4-tuples of real numbers.Understanding vector spaces is crucial for linear algebra problems, as they form the foundational structure within which vectors exist and interact.