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23.7. Examples
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Today, we're going to evaluate whether a set of vectors is linearly independent. Let's consider the vectors v1 = [1, 2, 3], v2 = [4, 5, 6], and v3 = [7, 8, 9]. Can anyone tell me the first step to check their independence?
Do we need to form a matrix with these vectors?
Exactly! We form the matrix A with these vectors as rows. Let’s write it out: A = [[1,4,7], [2,5,8], [3,6,9]]. Now, who can remember how to use row reduction?
We need to simplify it until we get to row echelon form, right?
Correct! Once we perform row reduction, we notice a row of zeros appears, which signals linear dependence. What does this mean for the set?
It means one of the vectors can be expressed as a combination of the others!
Good job! This insight leads us to conclude that the set is linearly dependent.
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Now let’s examine another example. We have the standard basis vectors for R3: v1 = [1, 0, 0], v2 = [0, 1, 0], and v3 = [0, 0, 1]. How can we determine if these vectors are linearly independent?
Since they are all different and point in different directions, I think they are independent.
That's a great observation! Let's prove it formally by also forming a matrix and demonstrating through row reduction that each vector contributes uniquely to the space.
So each vector remains distinct and does not rely on the others to form the space?
Precisely! This means they span R3 and are linearly independent since no vector can be written as a combination of the others.
Got it! So in R3, we need three independent vectors to span the space.
Exactly! This underscores the significance of linear independence in vector spaces.
Overview
Short Summary
This section provides practical examples to test the linear independence of given sets of vectors using matrix operations.
Medium Summary
In this section, we explore two examples to determine the linear independence of given vectors. The first example illustrates a set of vectors that are linearly dependent, while the second demonstrates a set that is linearly independent, employing techniques like row reduction and algebraic definitions.
Detailed Summary
Detailed Summary
In Section 23.7, we delve into examples that illustrate the application of the concept of linear independence within vector spaces. The first example involves examining three vectors:
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Upon forming a matrix with these vectors as rows and executing row reduction, we find that the rank is less than the number of vectors, determining that these vectors are linearly dependent. The second example checks another set of vectors corresponding to the standard basis of :
- .
Through visualizing their geometric representation, we validate their linear independence as they span the entire space. This section reinforces the foundational principles of linear independence through practical examples, offering a tangible grasp of the concepts and inviting students to engage actively with the material.
Reference YouTube Videos
Audio Book
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Create a free accountExample 1 Check if the vectors
[1] [4] [7]
are linearly independent. Solution: Form the matrix: \[ A = \begin{bmatrix} 1 & 4 & 7 \\ 2 & 5 & 8 \\ 3 & 6 & 9 \end{bmatrix} $$ Row reduce: $$ \begin{bmatrix} 1 & 4 & 7 \\ 2 & 5 & 8 \\ 3 & 6 & 9 \end{bmatrix} \to \begin{bmatrix} 1 & 4 & 7 \\ 0 & -3 & -6 \\ 0 & -6 & -12 \end{bmatrix} \to \begin{bmatrix} 1 & 4 & 7 \\ 0 & -3 & -6 \\ 0 & 0 & 0 \end{bmatrix} $$ Rank = 2 < 3 → Linearly dependentDetailed Explanation
In this example, we are asked to determine if a set of vectors is linearly independent. We start by constructing a matrix using the vectors. Then we perform row reduction (a type of simplified arithmetic operations on matrices) to find the reduced row echelon form. If the rank (the number of non-zero rows) of the matrix is less than the number of vectors, then the vectors are linearly dependent, meaning at least one can be formed by a combination of the others. Here, we found the rank to be 2, which is less than 3, indicating that the vectors are linearly dependent.
Examples & Analogies
Think of a team of three people and their combined skills. If one of them has skills that can be entirely provided by the other two (like someone who can only support but not lead), then not all three are necessary for the task. Hence, they are similar to linearly dependent vectors.
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Create a free accountExample 2 Determine if
[1] [0] [0] [\text{\textbf{v}}_1 = \begin{bmatrix} 1 \ 0 \ 0 \end{bmatrix}, \text{\textbf{v}}_2 = \begin{bmatrix} 0 \ 1 \ 0 \end{bmatrix}, \text{\textbf{v}}_3 = \begin{bmatrix} 0 \ 0 \ 1 \end{bmatrix}
are linearly independent.
This is the standard basis of R3, and clearly linearly independent.
Detailed Explanation
In this example, we are testing three vectors corresponding to the standard basis of R³. These vectors are represented as unit vectors in each of the three dimensions (x, y, z). Because each vector points in a unique direction and cannot be expressed as combinations of the others, they are linearly independent. This implies that they can be used to represent any vector in R³ uniquely.
Examples & Analogies
Imagine a 3D space where you need three arrows to point in three different directions—one for up, one for right, and one for forward. Each arrow represents a unique direction, and together they can point to any location in space—this is how the standard basis vectors function in linear algebra.
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Key concepts
Core takeaways and short definitions to help you quickly recall the key ideas from this section.
- Linear Independence:
A set of vectors is independent if the only solution to their combination being zero is all coefficients are zero.
- Linear Dependence:
Indicates redundancy among vectors where at least one vector can be expressed in terms of others.
- Row Reduction:
A technique to analyze the relationships among vectors through matrix manipulation.
Examples
Step-by-step examples to apply the section's ideas and test your understanding.
Example 1: For vectors [1, 2, 3], [4, 5, 6], and [7, 8, 9], the matrix formed is row reduced to show they are dependent.
Example 2: The vectors [1, 0, 0], [0, 1, 0], and [0, 0, 1] are independent as they span R3 without redundancy.
Memory aids
Imagine three friends trying to form a band; if one always plays the same tune as another, their band is off-key, hence dependent.
To remember linear combinations, think of 'Wavy V' for 'What About Vector Independence?'
Flash Cards
Glossary
Linear Independence
A set of vectors is linearly independent if the only solution to their linear combination equating to zero is the trivial solution where all coefficients are zero.
Linear Dependence
A set of vectors is linearly dependent if at least one vector can be expressed as a linear combination of the others.
Row Reduction
A process used to simplify matrices into row echelon form, allowing for the evaluation of linear independence.