Solution LI.C60 Robert Beezer
Theorem BNS says that if we find the vector form of the solutions to the homogeneous system $\homosystem{A}$, then the fixed vectors (one per free variable) will have the desired properties. Row-reduce $A$, viewing it as the augmented matrix of a homogeneous system with an invisible columns of zeros as the last column, \begin{equation*} \begin{bmatrix} \leading{1} & 0 & 4 & -5\\ 0 & \leading{1} & 2 & -3\\ 0 & 0 & 0 & 0 \end{bmatrix} \end{equation*} Moving to the vector form of the solutions (Theorem VFSLS), with free variables $x_3$ and $x_4$, solutions to the consistent system (it is homogeneous, Theorem HSC) can be expressed as \begin{equation*} \colvector{x_1\\x_2\\x_3\\x_4} = x_3\colvector{-4\\-2\\1\\0}+ x_4\colvector{5\\3\\0\\1} \end{equation*} Then with $S$ given by \begin{equation*} S=\set{\colvector{-4\\-2\\1\\0},\,\colvector{5\\3\\0\\1}} \end{equation*} Theorem BNS guarantees the set has the desired properties.