Math Problem Statement

Let A be a 3 × 3 matrix such that B = { [2, -3, 0], [-4, 2, 0] } is a basis of Null(A). Find a non-zero vector v ∈ Row(A).

Solution

To solve the problem provided, let’s analyze the given details and find a solution.

Given Information:

  • A 3×33 \times 3 matrix AA is given.
  • The null space (Null(A)\text{Null}(A)) of AA has a basis: B={[230],[420]}B = \left\{ \begin{bmatrix} 2 \\ -3 \\ 0 \end{bmatrix}, \begin{bmatrix} -4 \\ 2 \\ 0 \end{bmatrix} \right\}
  • We need to find a non-zero vector v\mathbf{v} in the row space of AA (Row(A)\text{Row}(A)).

Key Observations:

  1. Since the null space of AA is spanned by the given vectors, the dimension of Null(A)\text{Null}(A) is 2.

  2. By the Rank-Nullity Theorem: dim(Row(A))+dim(Null(A))=number of columns of A.\text{dim}(\text{Row}(A)) + \text{dim}(\text{Null}(A)) = \text{number of columns of } A. For AA, the number of columns is 3. Therefore: dim(Row(A))=32=1.\text{dim}(\text{Row}(A)) = 3 - 2 = 1. Thus, the row space is one-dimensional, and any vector in the row space will be a scalar multiple of a single row vector.

  3. Any vector v\mathbf{v} in Row(A)\text{Row}(A) will satisfy: vn=0,\mathbf{v} \cdot \mathbf{n} = 0, where n\mathbf{n} is any vector in Null(A)\text{Null}(A). This is because Null(A)\text{Null}(A) is orthogonal to Row(A)\text{Row}(A).


Approach:

To find a non-zero vector vRow(A)\mathbf{v} \in \text{Row}(A):

  1. Let v=[v1v2v3]\mathbf{v} = \begin{bmatrix} v_1 \\ v_2 \\ v_3 \end{bmatrix}.
  2. Enforce the orthogonality condition for the null space basis vectors: v[230]=0andv[420]=0.\mathbf{v} \cdot \begin{bmatrix} 2 \\ -3 \\ 0 \end{bmatrix} = 0 \quad \text{and} \quad \mathbf{v} \cdot \begin{bmatrix} -4 \\ 2 \\ 0 \end{bmatrix} = 0.
  3. These conditions give two equations: 2v13v2+0v3=0(1)2v_1 - 3v_2 + 0v_3 = 0 \quad \text{(1)} 4v1+2v2+0v3=0(2).-4v_1 + 2v_2 + 0v_3 = 0 \quad \text{(2)}.

Solve the System:

From equation (1): 2v13v2=0    v1=32v2.2v_1 - 3v_2 = 0 \implies v_1 = \frac{3}{2}v_2.

From equation (2): 4v1+2v2=0    4(32v2)+2v2=0.-4v_1 + 2v_2 = 0 \implies -4\left(\frac{3}{2}v_2\right) + 2v_2 = 0. Simplify: 6v2+2v2=0    4v2=0    v2=0.-6v_2 + 2v_2 = 0 \implies -4v_2 = 0 \implies v_2 = 0.

Substitute v2=0v_2 = 0 into v1=32v2v_1 = \frac{3}{2}v_2: v1=0.v_1 = 0.

Thus, v3v_3 can be any non-zero value. Choose v3=1v_3 = 1, and the vector becomes: v=[001].\mathbf{v} = \begin{bmatrix} 0 \\ 0 \\ 1 \end{bmatrix}.


Final Answer:

A non-zero vector vRow(A)\mathbf{v} \in \text{Row}(A) is: v=[001].\mathbf{v} = \begin{bmatrix} 0 \\ 0 \\ 1 \end{bmatrix}.


Would you like detailed verification or have further questions? Here are 5 related concepts to explore:

  1. What is the Rank-Nullity Theorem and how is it applied?
  2. How do we interpret the null space geometrically?
  3. How do orthogonality properties relate to the row and null spaces?
  4. What is the basis of the column space of a matrix?
  5. Can you find the rank of AA based on its null space?

Tip: Always verify the orthogonality of your solution when working with row and null spaces!

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Linear Algebra
Row Space
Null Space
Orthogonality
Basis and Dimension

Formulas

Rank-Nullity Theorem: dim(Row(A)) + dim(Null(A)) = number of columns of A
Orthogonality Condition: v ⋅ n = 0 where n is in Null(A) and v is in Row(A)

Theorems

Rank-Nullity Theorem

Suitable Grade Level

College level or advanced high school