Chapter 2: Problem 14
Describe the span of the given vectors (a) geometrically and (b) algebraically. $$\left[\begin{array}{l} 0 \\ 0 \end{array}\right],\left[\begin{array}{l} 3 \\ 4 \end{array}\right]$$
Short Answer
Expert verified
The span is a line through the origin along \( \begin{bmatrix} 3 \\ 4 \end{bmatrix} \).
Step by step solution
01
Introduce the Vectors
We have two vectors: \( \mathbf{v_1} = \begin{bmatrix} 0 \ 0 \end{bmatrix} \) and \( \mathbf{v_2} = \begin{bmatrix} 3 \ 4 \end{bmatrix} \). These vectors are in a 2-dimensional space.
02
Understanding Span Geometrically
Geometrically, the span of a set of vectors is the set of all points that can be reached by a linear combination of the vectors. The zero vector alone, \( \mathbf{v_1} \), does not contribute to the span direction as it represents a point at the origin. The vector \( \mathbf{v_2} \) determines a line through the origin in the direction of \( \begin{bmatrix} 3 \ 4 \end{bmatrix} \). Thus, the span forms a line.
03
Understanding Span Algebraically
Algebraically, the span of \( \mathbf{v_1} \) and \( \mathbf{v_2} \) is the set of all vectors that can be written as a linear combination of \( \mathbf{v_1} \) and \( \mathbf{v_2} \), i.e., \( c_1 \cdot \mathbf{v_1} + c_2 \cdot \mathbf{v_2} \) where \( c_1 \) and \( c_2 \) are scalars. Since \( \mathbf{v_1} \) contributes nothing (it is zero), the span reduces to vectors of the form \( c_2 \cdot \begin{bmatrix} 3 \ 4 \end{bmatrix} \), which represents a line through the origin along \( \mathbf{v_2} \).
04
Conclusion
The geometric interpretation involves a line through the origin in the direction given by the vector \( \begin{bmatrix} 3 \ 4 \end{bmatrix} \). Algebraically, it consists of all vectors that are scalar multiples of \( \begin{bmatrix} 3 \ 4 \end{bmatrix} \), confirming that the span is a line.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Geometric Interpretation
Vectors in geometry are depicted as arrows in a coordinate space, originating from the origin or another point. In this context, the **geometric interpretation** of the span of vectors focuses on what regions or lines these vectors create in space. For the vectors \( \mathbf{v_1} = \begin{bmatrix} 0 \ 0 \end{bmatrix} \) and \( \mathbf{v_2} = \begin{bmatrix} 3 \ 4 \end{bmatrix} \):
- \( \mathbf{v_1} \) is the zero vector. It represents a point at the origin (0,0) and does not define a direction or span any line or plane.
- \( \mathbf{v_2} \) is a vector that points towards the coordinates (3,4). This creates a straight line when extended in both directions through the origin.
Algebraic Representation
The **algebraic representation** of the span of vectors describes all the possible vector combinations that can be formed using a set of given vectors. To understand the span through algebraic terms, consider any linear combination of vectors \( \mathbf{v_1} \) and \( \mathbf{v_2} \):
- Any vector in the span can be expressed as \( c_1 \cdot \mathbf{v_1} + c_2 \cdot \mathbf{v_2} \), with \( c_1 \) and \( c_2 \) being scalar values.
- Specifically, because \( \mathbf{v_1} = \begin{bmatrix} 0 \ 0 \end{bmatrix} \), the zero vector contributes nothing to the directionality or extent of the span.
- This simplifies the algebraic expression to \( c_2 \cdot \begin{bmatrix} 3 \ 4 \end{bmatrix} \).
Linear Combinations
**Linear combinations** involve combining vectors together using scalar multiplication and addition. The concept is central to understanding spans and other vector space elements. The process of forming linear combinations is easy:
- Each given vector is multiplied by a scalar (a real number), which stretches or shrinks the vector.
- The results from this multiplication are then added together to form a new vector.
- The expression \( c_1 \cdot \begin{bmatrix} 0 \ 0 \end{bmatrix} + c_2 \cdot \begin{bmatrix} 3 \ 4 \end{bmatrix} \) uses both operations to combine the vectors.
- Here, since \( c_1 \cdot \begin{bmatrix} 0 \ 0 \end{bmatrix} \) remains zero, the overall equation simplifies based on the scaling of \( \mathbf{v_2} \) by scalar \( c_2 \).