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Problem 176

Let \(\mathrm{P}_{4}\), denote the vector space of all polynomials of degree at most equal to four. Let \(\mathrm{V}\) be the subspace of \(\mathrm{P}_{4}\). spanned by $\mathrm{S}=\left\\{\alpha_{1}, \alpha_{2}, \alpha_{3}, \alpha_{4}\right\\}\( where \)\alpha_{1}=\mathrm{t}^{4}+\mathrm{t}^{2}+2 \mathrm{t}+1$ \(\alpha_{2}=t^{4}+t^{2}+2 t+2, \alpha_{3}=2 t^{4}+t^{3}+t+2\) and \(\alpha_{4}=t^{4}+t^{3}-t^{2}\) \(-\mathrm{t}\). Find a basis for \(\mathrm{V}\).

Short Answer

Expert verified
The basis for subspace V is the set B = { \(α_1, α_3, α_4\) }, where \(α_1 = t^4 + 2t^3 + t^2 + 1\), \(α_3 = -\frac{1}{3}(-3t^3 - 2t^2 + t)\), and \(\alpha_4 = -t + 1\).
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Step 1: Set up the matrix A from S

Construct a matrix A using the coefficients of the given polynomials in the set S as row vectors. A = $\begin{pmatrix} 1 & 2 & 1 & 0 & 1\\ 1 & 2 & 1 & 0 & 1\\ 2 & 1 & 0 & 1 & 2\\ 1 & -1 & -1 & 1 & 0 \end{pmatrix}$

Step 2: Perform Gaussian elimination on matrix A

To find linearly independent polynomials, we need to perform Gaussian elimination (row reduction) on the matrix A. Row 2 can be eliminated, since it is the same as Row 1. Let's also eliminate Row 4: R4 - R1 -> R4 This results in the following matrix: A = $\begin{pmatrix} 1 & 2 & 1 & 0 & 1\\ 0 & 0 & 0 & 0 & 0\\ 2 & 1 & 0 & 1 & 2\\ 0 & -3 & -2 & 1 & -1 \end{pmatrix}$ Now, eliminate Row 3: R3 - 2*R1 -> R3 This leads to the following matrix: A = $\begin{pmatrix} 1& 2 & 1 & 0 & 1\\ 0 & 0 & 0 & 0 & 0\\ 0 & -3 & -2 & 1 & 0\\ 0 & -3 & -2 & 1 & -1 \end{pmatrix}$ Finally, we can eliminate Row 4: R4 - R3 -> R4 This results in the following matrix: A = $\begin{pmatrix} 1 & 2 & 1 & 0 & 1\\ 0 & 0 & 0 & 0 & 0\\ 0 & -3 & -2 & 1 & 0\\ 0 & 0 & 0 & 0 & 1 \end{pmatrix}$

Step 3: Determine the basis for subspace V

Now that our matrix A is in row echelon form, we can determine the basis for subspace V. The non-zero rows of the matrix A correspond to linearly independent polynomials in the set S. According to the row reduced matrix, the linearly independent polynomials are: \(α_1 = t^4 + 2t^3 + t^2 + 1\) \(α_3 = -\frac{1}{3}(-3t^3 - 2t^2 + t)\) \(\alpha_4 = -t + 1\) So, the basis for subspace V is the set: B = { \(α_1, α_3, α_4\) } This basis consists of three linearly independent polynomials that span the subspace V.

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Most popular questions from this chapter

Chapter 7

Let \(\mathrm{V}\) be the subspace of \(\mathrm{R}^{4}\) spanned by $\mathrm{S}=\left\\{\alpha_{1}, \alpha_{2}, \alpha_{3}, \alpha_{4}, \alpha_{5}\right\\}\( where \)\alpha_{1}=[1,2,1,2], \alpha_{2}=[2,1,2,1]$ \(\alpha_{3}=[3,2,3,2], \alpha_{4}=[3,3,3,3], \alpha_{5}=[5,3,5,3]\). Find a basis for \(\mathrm{V}\).

Chapter 7

Find the rank of matrix A where: $\begin{array}{rrrrr}\text { (i) } \mathrm{A}= & \mid 1 & 3 & 1 & -2 & -3 \mid \\\ & 11 & 4 & 3 & -1 & -4 \\ & 2 & 3 & -4 & -7 & -3 \\ & 13 & 8 & 1 & -7 & -8\end{array}$ (ii) $\begin{array}{rrr}\mathrm{A}= & \mid \begin{array}{rrr}1 & 2 & -3\end{array} \\ & \mid 2 & 1 & 0 \\ & \mid-2 & -1 & 3 \mid \\ & -1 & 4 & -2\end{array}$ (iii) $\begin{array}{rr}\mathrm{A}= & \mid 1 & 3 \mid \\ & \mid 0 & -2 \mid \\\ & \mid 5 & -1 \\ & \mid-2 & 3\end{array} \mid$

Chapter 7

Give an example to illustrate the following theorem: The system of n homogeneous linear equations in \(\mathrm{n}\) unknowns, \(\mathrm{AX}=0\), has a nontrivial solution if and only if rank \(\mathrm{A}<\mathrm{n}\)

Chapter 7

Show that the matrix $$ \mathrm{A}=\begin{array}{cll} 0 & 1 & 2 \\ 2 & 3 & 4 \\ 14 & 7 & 10 \end{array} $$ is equivalent to \(\mathrm{D}^{33}{ }_{2}\) where $\mathrm{D}^{\mathrm{m}, \mathrm{n}} \mathrm{r}$ denotes the canonical form under equivalence of A. D \(^{\mathrm{m}, \mathrm{n}}_{\mathrm{r}}\) is the echelon form that has one's along the diagonal and zeros elsewhere, and where all the zero rows are consigned to the depths of the matrix.

Chapter 7

Let \(\mathrm{A}\) be the matrix $$ \begin{array}{rrrrrr} \mid 0 & 1 & 3 & -2 & -1 & 2 \\ 10 & 2 & 6 & -4 & -2 & 4 \\ \mid 0 & 1 & 3 & -2 & 1 & 4 \\ \mid 0 & 2 & 6 & 1 & -1 & 0 \end{array} $$ Find the determinant rank of \(\mathrm{A}\)

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