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[M] According to Theorem 11, a linearly independent set \(\left\{ {{{\bf{v}}_1},....{{\bf{v}}_k}} \right\}\) in \({\mathbb{R}^n}\) can be expanded to a basis for \({\mathbb{R}^n}\). One way to this is to create \(A = \left[ {\begin{array}{*{20}{c}}{{{\bf{v}}_1}}& \cdots &{{{\bf{v}}_k}\,\;\,\begin{array}{*{20}{c}}{{{\bf{e}}_1}}& \cdots &{{{\bf{e}}_n}}\end{array}}\end{array}} \right]\), with \({{\bf{e}}_1}\),….,\({{\bf{e}}_n}\) the columns of identity matrix; the pivot columns of A form a basis for \({\mathbb{R}^n}\).

a. Use the method described to extend the following vectors to a basis for \({\mathbb{R}^5}\).

\({{\bf{v}}_1} = \left[ {\begin{array}{*{20}{c}}{ - {\bf{9}}}\\{ - {\bf{7}}}\\{\bf{8}}\\{ - {\bf{5}}}\\{\bf{7}}\end{array}} \right]\), \({{\bf{v}}_2} = \left[ {\begin{array}{*{20}{c}}{\bf{9}}\\{\bf{4}}\\{\bf{1}}\\{\bf{6}}\\{ - {\bf{7}}}\end{array}} \right]\), \({{\bf{v}}_3} = \left[ {\begin{array}{*{20}{c}}{\bf{6}}\\{\bf{7}}\\{ - {\bf{8}}}\\{\bf{5}}\\{ - {\bf{7}}}\end{array}} \right]\)

b. Explain why the method works in general: Why are the original vectors \({{\bf{v}}_1}\),….,\({{\bf{v}}_k}\) included in the basis found for Col A? Why is \({\bf{Col}}\,A = {\mathbb{R}^n}\)?

Short Answer

Expert verified

a. \(\left\{ {{{\bf{v}}_1},\,\,{{\bf{v}}_2},\;\;{{\bf{v}}_3},\;\;{{\bf{e}}_2},\;{{\bf{e}}_3}} \right\}\)

b. \({\rm{Col}}\left( A \right) = {\mathbb{R}^n}\)

Step by step solution

01

Form the matrix using vectors

The matrix using vectors can be written as:

\(A = \left[ {\begin{array}{*{20}{c}}{ - 9}&9&6\\{ - 7}&4&7\\8&1&{ - 8}\\{ - 5}&6&5\\7&{ - 7}&{ - 7}\end{array}} \right]\)

02

Find the matrix \(\left[ {\begin{array}{*{20}{c}}A&{{I_{\bf{5}}}}\end{array}} \right]\)

The matrix \(\left[ {\begin{array}{*{20}{c}}A&{{I_5}}\end{array}} \right]\) can be expressed as:

\(\left[ {\begin{array}{*{20}{c}}A&{{I_5}}\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}{ - 9}&9&6\\{ - 7}&4&7\\8&1&{ - 8}\\{ - 5}&6&5\\7&{ - 7}&{ - 7}\end{array}\,\,\,\,\,\begin{array}{*{20}{c}}1&0&0&0&0\\0&1&0&0&0\\0&0&1&0&0\\0&0&0&1&0\\0&0&0&0&1\end{array}} \right]\)

03

Find the row reduced echelon form of \(\left[ {\begin{array}{*{20}{c}}A&{{I_{\bf{5}}}}\end{array}} \right]\)

Let

\(B = \left[ {\begin{array}{*{20}{c}}{ - 9}&9&6\\{ - 7}&4&7\\8&1&{ - 8}\\{ - 5}&6&5\\7&{ - 7}&{ - 7}\end{array}\,\,\,\,\,\begin{array}{*{20}{c}}1&0&0&0&0\\0&1&0&0&0\\0&0&1&0&0\\0&0&0&1&0\\0&0&0&0&1\end{array}} \right]\).

Use the following MATLAB code to find the row reduce echelon form:

\(\begin{array}{l} > > B = \left[ { - 9\,\,9\,\,6\,\,1\,\,0\,\,0\,\,0\,\,0;\,\, - 7\,\,4\,\,7\,\,0\,\,1\,\,0\,\,0\,\,0\,;\,\,8\,\,1\,\, - 8\,\,0\,\,0\,\,1\,\,0\,\,0;\,\, - 5\,\,6\,\,5\,\,0\,\,0\,\,0\,\,1\,\,0;\,\,7\,\, - 7\,\, - 7\,\,0\,\,0\,\,0\,\,0\,\,1} \right];\\ > > U = {\rm{rref}}\left( A \right)\end{array}\)\(\left[ {\begin{array}{*{20}{c}}{ - 9}&9&6\\{ - 7}&4&7\\8&1&{ - 8}\\{ - 5}&6&5\\7&{ - 7}&{ - 7}\end{array}\,\,\,\,\,\begin{array}{*{20}{c}}1&0&0&0&0\\0&1&0&0&0\\0&0&1&0&0\\0&0&0&1&0\\0&0&0&0&1\end{array}} \right] \sim \left[ {\begin{array}{*{20}{c}}1&0&0\\0&1&0\\0&0&1\\0&0&0\\0&0&0\end{array}\,\,\,\,\,\,\begin{array}{*{20}{c}}{ - \frac{1}{3}}&0&0&1&{\frac{3}{7}}\\0&0&0&1&{\frac{5}{7}}\\{ - \frac{1}{3}}&0&0&0&{ - \frac{3}{7}}\\0&1&0&3&{\frac{{22}}{7}}\\0&0&1&0&{ - \frac{{53}}{7}}\end{array}} \right]\)

As the pivot columns are 1, 2, 3, 5, and 6, the extended basis is:

\(\left\{ {{{\bf{v}}_1},\,\,{{\bf{v}}_2},\;\;{{\bf{v}}_3},\;\;{{\bf{e}}_2},\;{{\bf{e}}_3}} \right\}\)

04

Check why Col A\( = {\mathbb{R}^n}\)

If the set \(\left\{ {{{\bf{v}}_1},\;{{\bf{v}}_2},\;....,\;{{\bf{v}}_k}} \right\}\) is linearly independent, there is a pivot element in each column. Therefore,

\({\rm{Col}}\left( A \right) = {\mathbb{R}^n}\)

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Most popular questions from this chapter

Is it possible for a nonhomogeneous system of seven equations in six unknowns to have a unique solution for some right-hand side of constants? Is it possible for such a system to have a unique solution for every right-hand side? Explain.

In Exercise 18, Ais an \(m \times n\) matrix. Mark each statement True or False. Justify each answer.

18. a. If B is any echelon form of A, then the pivot columns of B form a basis for the column space of A.

b. Row operations preserve the linear dependence relations among the rows of A.

c. The dimension of the null space of A is the number of columns of A that are not pivot columns.

d. The row space of \({A^T}\) is the same as the column space of A.

e. If A and B are row equivalent, then their row spaces are the same.

Exercises 23-26 concern a vector space V, a basis \(B = \left\{ {{{\bf{b}}_{\bf{1}}},....,{{\bf{b}}_n}\,} \right\}\) and the coordinate mapping \({\bf{x}} \mapsto {\left( {\bf{x}} \right)_B}\).

Show that a subset \(\left\{ {{{\bf{u}}_1},...,{{\bf{u}}_p}} \right\}\) in V is linearly independent if and only if the set of coordinate vectors \(\left\{ {{{\left( {{{\bf{u}}_{\bf{1}}}} \right)}_B},.....,{{\left( {{{\bf{u}}_p}} \right)}_B}} \right\}\) is linearly independent in \({\mathbb{R}^n}\)(Hint: Since the coordinate mapping is one-to-one, the following equations have the same solutions, \({c_{\bf{1}}}\),….,\({c_p}\))

\({c_{\bf{1}}}{{\bf{u}}_{\bf{1}}} + ..... + {c_p}{{\bf{u}}_p} = {\bf{0}}\) The zero vector V

\({\left( {{c_{\bf{1}}}{{\bf{u}}_{\bf{1}}} + ..... + {c_p}{{\bf{u}}_p}} \right)_B} = {\left( {\bf{0}} \right)_B}\) The zero vector in \({\mathbb{R}^n}\)a

Find a basis for the set of vectors in\({\mathbb{R}^{\bf{2}}}\)on the line\(y = {\bf{5}}x\).

(M) Show thatis a linearly independent set of functions defined on. Use the method of Exercise 37. (This result will be needed in Exercise 34 in Section 4.5.)

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