Solution VR.C10 Robert Beezer
We need to express the vector $\vect{v}$ as a linear combination of the vectors in $B$. Theorem VRRB tells us we will be able to do this, and do it uniquely. The vector equation \begin{equation*} a_1\colvector{2\\-2\\2}+ a_2\colvector{1\\3\\1}+ a_3\colvector{3\\5\\2} = \colvector{11\\5\\8} \end{equation*} becomes (via Theorem SLSLC) a system of linear equations with augmented matrix, \begin{equation*} \begin{bmatrix} 2 & 1 & 3 & 11\\ -2 & 3 & 5 & 5\\ 2 & 1 & 2 & 8 \end{bmatrix} \end{equation*} This system has the unique solution $a_1=2$, $a_2=-2$, $a_3=3$. So by Definition VR, \begin{equation*} \vectrep{B}{\vect{v}}=\vectrep{B}{\colvector{11\\5\\8}} = \vectrep{B}{ 2\colvector{2\\-2\\2}+ (-2)\colvector{1\\3\\1}+ 3\colvector{3\\5\\2} } =\colvector{2\\-2\\3} \end{equation*}