Solution FS.C25 Robert Beezer
Add a $4\times 4$ identity matrix to the right of $A$ to form the matrix $M$ and then row-reduce to the matrix $N$, \begin{equation*} M= \begin{bmatrix} -5 & 3 & -1 & 1 & 0 & 0 & 0 \\ -1 & 1 & 1 & 0 & 1 & 0 & 0 \\ -8 & 5 & -1 & 0 & 0 & 1 & 0 \\ 3 & -2 & 0 & 0 & 0 & 0 & 1 \end{bmatrix} \rref \begin{bmatrix} \leading{1} & 0 & 2 & 0 & 0 & -2 & -5 \\ 0 & \leading{1} & 3 & 0 & 0 & -3 & -8 \\ 0 & 0 & 0 & \leading{1} & 0 & -1 & -1 \\ 0 & 0 & 0 & 0 & \leading{1} & 1 & 3 \end{bmatrix} =N \end{equation*} To apply Theorem FS in each of these four parts, we need the two matrices, \begin{align*} C&= \begin{bmatrix} \leading{1} & 0 & 2 \\ 0 & \leading{1} & 3 \end{bmatrix} & L&= \begin{bmatrix} \leading{1} & 0 & -1 & -1 \\ 0 & \leading{1} & 1 & 3 \end{bmatrix} \end{align*} (a) \begin{align*} \rsp{A} &=\rsp{C}&&\knowl{./knowls/theorem.FS.knowl}{\text{Theorem FS}}\\ &=\spn{\set{\colvector{1\\0\\2},\,\colvector{0\\1\\3}}}&&\knowl{./knowls/theorem.BRS.knowl}{\text{Theorem BRS}} \end{align*} (b) \begin{align*} \csp{A} &=\nsp{L}&&\knowl{./knowls/theorem.FS.knowl}{\text{Theorem FS}}\\ &=\spn{\set{\colvector{1\\-1\\1\\0},\,\colvector{1\\-3\\0\\1}}}&&\knowl{./knowls/theorem.BNS.knowl}{\text{Theorem BNS}} \end{align*} (c) \begin{align*} \nsp{A} &=\nsp{C}&&\knowl{./knowls/theorem.FS.knowl}{\text{Theorem FS}}\\ &=\spn{\set{\colvector{-2\\-3\\1}}}&&\knowl{./knowls/theorem.BNS.knowl}{\text{Theorem BNS}} \end{align*} (d) \begin{align*} \lns{A} &=\rsp{L}&&\knowl{./knowls/theorem.FS.knowl}{\text{Theorem FS}}\\ &=\spn{\set{\colvector{1\\0\\-1\\-1},\,\colvector{0\\1\\1\\3}}}&&\knowl{./knowls/theorem.BRS.knowl}{\text{Theorem BRS}} \end{align*}