Suppose B is a 5 x 5 matrix and Nul B is NOT the zero subspace. Do you have enough information to determine if Col B equals R5? Why or why not?

Advanced Engineering Mathematics
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Chapter2: Second-order Linear Odes
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**Title: Understanding Column Spaces in Linear Algebra**

**Problem:**

Suppose \( B \) is a \( 5 \times 5 \) matrix and \(\text{Nul } B\) is NOT the zero subspace. Do you have enough information to determine if \(\text{Col } B\) equals \(\mathbb{R}^5\)? Why or why not?

**Explanation:**

To determine whether the column space of the matrix \( B \) (denoted as \(\text{Col } B\)) equals \(\mathbb{R}^5\), we need to assess the concept of linear independence and the rank of the matrix \( B \).

- **Key Concept: Rank-Nullity Theorem**

  The rank-nullity theorem states that for any matrix \( A \) of size \( m \times n \), the sum of the rank and the nullity (dimension of the null space) equals \( n\):
  \[
  \text{rank}(A) + \text{nullity}(A) = n
  \]

- **Implication for the 5x5 Matrix \( B \)**

  Given that \(\text{Nul } B\) is NOT the zero subspace, it means that the nullity of \( B \) is greater than 0. Thus, the rank of \( B \) is less than 5.

- **Effect on Column Space**

  For \(\text{Col } B\) to equal \(\mathbb{R}^5\), the rank of \( B \) must be 5. However, because the nullity is greater than 0, the rank must be less than 5. Therefore, \(\text{Col } B\) cannot equal \(\mathbb{R}^5\).

**Conclusion:**

No, we do not have enough information to say \(\text{Col } B\) equals \(\mathbb{R}^5\). In fact, with the given condition that \(\text{Nul } B\) is NOT the zero subspace, we can definitively conclude that \(\text{Col } B\) does not, and cannot, equal \(\mathbb{R}^5\).
Transcribed Image Text:**Title: Understanding Column Spaces in Linear Algebra** **Problem:** Suppose \( B \) is a \( 5 \times 5 \) matrix and \(\text{Nul } B\) is NOT the zero subspace. Do you have enough information to determine if \(\text{Col } B\) equals \(\mathbb{R}^5\)? Why or why not? **Explanation:** To determine whether the column space of the matrix \( B \) (denoted as \(\text{Col } B\)) equals \(\mathbb{R}^5\), we need to assess the concept of linear independence and the rank of the matrix \( B \). - **Key Concept: Rank-Nullity Theorem** The rank-nullity theorem states that for any matrix \( A \) of size \( m \times n \), the sum of the rank and the nullity (dimension of the null space) equals \( n\): \[ \text{rank}(A) + \text{nullity}(A) = n \] - **Implication for the 5x5 Matrix \( B \)** Given that \(\text{Nul } B\) is NOT the zero subspace, it means that the nullity of \( B \) is greater than 0. Thus, the rank of \( B \) is less than 5. - **Effect on Column Space** For \(\text{Col } B\) to equal \(\mathbb{R}^5\), the rank of \( B \) must be 5. However, because the nullity is greater than 0, the rank must be less than 5. Therefore, \(\text{Col } B\) cannot equal \(\mathbb{R}^5\). **Conclusion:** No, we do not have enough information to say \(\text{Col } B\) equals \(\mathbb{R}^5\). In fact, with the given condition that \(\text{Nul } B\) is NOT the zero subspace, we can definitively conclude that \(\text{Col } B\) does not, and cannot, equal \(\mathbb{R}^5\).
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