Chapter 1: Problem 27
Is it possible for a singular matrix \(B\) to be row equivalent to a nonsingular matrix \(A\) ? Explain.
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Chapter 1: Problem 27
Is it possible for a singular matrix \(B\) to be row equivalent to a nonsingular matrix \(A\) ? Explain.
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Find the inverse of each of the following matrices: (a) \(\left(\begin{array}{rr}-1 & 1 \\ 1 & 0\end{array}\right)\) (b) \(\left(\begin{array}{ll}2 & 5 \\ 1 & 3\end{array}\right)\) (c) \(\left(\begin{array}{ll}2 & 6 \\ 3 & 8\end{array}\right)\) (d) \(\left(\begin{array}{ll}3 & 0 \\ 9 & 3\end{array}\right)\) (e) \(\left(\begin{array}{lll}1 & 1 & 1 \\ 0 & 1 & 1 \\ 0 & 0 & 1\end{array}\right)\) (f) \(\left(\begin{array}{lll}2 & 0 & 5 \\ 0 & 3 & 0 \\ 1 & 0 & 3\end{array}\right)\) (g) \(\left(\begin{array}{rrr}-1 & -3 & -3 \\ 2 & 6 & 1 \\ 3 & 8 & 3\end{array}\right)\) (h) \(\left(\begin{array}{rrr}1 & 0 & 1 \\ -1 & 1 & 1 \\ -1 & -2 & -3\end{array}\right)\)
For each of the systems of equations that follow, use Gaussian elimination to obtain an equivalent system whose coefficient matrix is in row echelon form. Indicate whether the system is consistent. If the system is consistent and involves no free variables, use back substitution to find the unique solution. If the system is consistent and there are free variables, transform it to reduced row echelon form and find all solutions $$\begin{aligned} &\text { (a) } \quad x_{1}-2 x_{2}=3\\\ &2 x_{1}-x_{2}=9 \end{aligned}$$ $$\begin{aligned} &\text { (b) } \quad 2 x_{1}-3 x_{2}=5\\\ &-4 x_{1}+6 x_{2}=8 \end{aligned}$$ $$\begin{aligned} &\text { (c) } \quad x_{1}+x_{2}=0\\\ &\begin{array}{l} 2 x_{1}+3 x_{2}=0 \\ 3 x_{1}-2 x_{2}=0 \end{array} \end{aligned}$$ $$\begin{aligned} &\text { (d) } 3 x_{1}+2 x_{2}-x_{3}=4\\\ &\begin{array}{r} x_{1}-2 x_{2}+2 x_{3}=1 \\ 11 x_{1}+2 x_{2}+x_{3}=14 \end{array} \end{aligned}$$ $$\begin{aligned} &\text { (e) } 2 x_{1}+3 x_{2}+x_{3}=1\\\ &\begin{array}{r} x_{1}+x_{2}+x_{3}=3 \\ 3 x_{1}+4 x_{2}+2 x_{3}=4 \end{array} \end{aligned}$$ $$\begin{aligned} &\text { (f) } \quad x_{1}-x_{2}+2 x_{3}=4\\\ &\begin{array}{l} 2 x_{1}+3 x_{2}-x_{3}=1 \\ 7 x_{1}+3 x_{2}+4 x_{3}=7 \end{array} \end{aligned}$$ $$\begin{aligned} &\text { (g) } x_{1}+x_{2}+x_{3}+x_{4}=0\\\ &\begin{array}{l} 2 x_{1}+3 x_{2}-x_{3}-x_{4}=2 \\ 3 x_{1}+2 x_{2}+x_{3}+x_{4}=5 \\ 3 x_{1}+6 x_{2}-x_{3}-x_{4}=4 \end{array} \end{aligned}$$ $$\begin{aligned} &\text { (h) } \quad x_{1}-2 x_{2}=3\\\ &\begin{aligned} 2 x_{1}+x_{2} &=1 \\ -5 x_{1}+8 x_{2} &=4 \end{aligned} \end{aligned}$$ $$\begin{aligned} &\text { (i) } \quad-x_{1}+2 x_{2}-x_{3}=2\\\ &\begin{aligned} -2 x_{1}+2 x_{2}+x_{3} &=4 \\ 3 x_{1}+2 x_{2}+2 x_{3} &=5 \\ -3 x_{1}+8 x_{2}+5 x_{3} &=17 \end{aligned} \end{aligned}$$ $$\begin{aligned} &\text { (j) } \quad x_{1}+2 x_{2}-3 x_{3}+x_{4}=1\\\ &\begin{array}{r} -x_{1}-x_{2}+4 x_{3}-x_{4}=6 \\ -2 x_{1}-4 x_{2}+7 x_{3}-x_{4}=1 \end{array} \end{aligned}$$ $$\begin{aligned} &\text { (k) } x_{1}+3 x_{2}+x_{3}+x_{4}=3\\\ &\begin{array}{c} 2 x_{1}-2 x_{2}+x_{3}+2 x_{4}=8 \\ x_{1}-5 x_{2}+x_{4}=5 \end{array} \end{aligned}$$ $$\begin{aligned} &\text { (I) } \quad x_{1}-3 x_{2}+\quad x_{3}=1\\\ &\begin{aligned} 2 x_{1}+x_{2}-x_{3} &=2 \\ x_{1}+4 x_{2}-2 x_{3} &=1 \\ 5 x_{1}-8 x_{2}+2 x_{3} &=5 \end{aligned} \end{aligned}$$
The matrix \\[ A=\left(\begin{array}{ll} 1 & -1 \\ 1 & -1 \end{array}\right) \\] has the property that \(A^{2}=O .\) Is it possible for a nonzero symmetric \(2 \times 2\) matrix to have this property? Prove your answer.
Let \(U\) be an \(n \times n\) upper triangular matrix with nonzero diagonal entries. (a) Explain why \(U\) must be nonsingular. (b) Explain why \(U^{-1}\) must be upper triangular.
Prove that if \(A\) is row equivalent to \(B\), then \(B\) is row equivalent to \(A\)
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