Chapter 1: Problem 13
Given a homogeneous system of linear equations, if the system is overdetermined, what are the possibilities as to the number of solutions? Explain.
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Chapter 1: Problem 13
Given a homogeneous system of linear equations, if the system is overdetermined, what are the possibilities as to the number of solutions? Explain.
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Let \\[ A=\left(\begin{array}{rr} 1 & 1 \\ 2 & -1 \end{array}\right) \quad \text { and } \quad B=\left(\begin{array}{ll} 2 & 1 \\ 1 & 3 \end{array}\right) \\] (a) Calculate \(A \mathbf{b}_{1}\) and \(A \mathbf{b}_{2}\) (b) Calculate \(\overrightarrow{\mathbf{a}}_{1} B\) and \(\overrightarrow{\mathbf{a}}_{2} B\) (c) Multiply \(A B,\) and verify that its column vectors are the vectors in part (a) and its row vectors are the vectors in part (b).
For each of the following pairs of matrices, find an elementary matrix \(E\) such that \(A E=B:\) (a) \(A=\left(\begin{array}{lll}4 & 1 & 3 \\ 2 & 1 & 4 \\ 1 & 3 & 2\end{array}\right), B=\left(\begin{array}{lll}3 & 1 & 4 \\ 4 & 1 & 2 \\ 2 & 3 & 1\end{array}\right)\) (b) \(A=\left(\begin{array}{ll}2 & 4 \\ 1 & 6\end{array}\right), B=\left(\begin{array}{rr}2 & -2 \\ 1 & 3\end{array}\right)\) (c) \(A=\left(\begin{array}{rrr}4 & -2 & 3 \\ -2 & 4 & 2 \\ 6 & 1 & -2\end{array}\right)\) \(B=\left(\begin{array}{rrr}2 & -2 & 3 \\ -1 & 4 & 2 \\ 3 & 1 & -2\end{array}\right)\)
Perform each of the following block multiplications: (a) \(\left[\begin{array}{ccc|c}1 & 1 & 1 & -1 \\ 2 & 1 & 2 & -1\end{array}\right)\left(\begin{array}{rrr}4 & -2 & 1 \\ 2 & 3 & 1 \\ 1 & 1 & 2 \\ 1 & 2 & 3\end{array}\right)\) (b) \(\left(\begin{array}{rr}4 & -2 \\ 2 & 3 \\ \frac{1}{1} & 2\end{array}\right)\left(\begin{array}{rrr|r}1 & 1 & 1 & -1 \\ 2 & 1 & 2 & -1\end{array}\right)\) \((\mathbf{c})\left(\begin{array}{rr|rr}\frac{3}{5} & -\frac{4}{5} & 0 & 0 \\\ \frac{4}{5} & \frac{3}{5} & 0 & 0 \\ \hline 0 & 0 & 1 & 0\end{array}\right)\left(\begin{array}{rr|r}\frac{3}{5} & \frac{4}{5} & 0 \\\ -\frac{4}{5} & \frac{3}{5} & 0 \\ \hline 0 & 0 & 1 \\ 0 & 0 & 0\end{array}\right)\) (d) \(\left(\begin{array}{ccc|cc}0 & 0 & 1 & 0 & 0 \\ 0 & 1 & 0 & 0 & 0 \\ 1 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 1 \\ 0 & 0 & 0 & 1 & 0\end{array}\right)\left(\begin{array}{cc}1 & -1 \\ 2 & -2 \\ 3 & -3 \\ 4 & -4 \\ 5 & -5\end{array}\right)\)
Let \(B=A^{T} A .\) Show that \(b_{i j}=\mathbf{a}_{i}^{T} \mathbf{a}_{j}\)
Let $$A=\left(\begin{array}{ll} 5 & 3 \\ 3 & 2 \end{array}\right), B=\left(\begin{array}{ll} 6 & 2 \\ 2 & 4 \end{array}\right), C=\left(\begin{array}{rr} 4 & -2 \\ -6 & 3 \end{array}\right)$$ Solve each of the following matrix equations: (a) \(A X+B=C\) (b) \(X A+B=C\) (c) \(A X+B=X\) (d) \(X A+C=X\)
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