## Elementary Linear Algebra 7th Edition

(a) $$AB=\left[ \begin {array}{cc} 60&72\\ -20&-24 \\ 10&12\\ 60&72\end {array} \right] .$$ (b) $BA$ not defined.
Given $$A=\left[\begin{array}{r}{6} \\ {-2} \\ {1} \\ {6}\end{array}\right], \quad B=\left[\begin{array}{cc}{10} & {12 ]}\end{array}\right.$$ We have (a) \begin{align*} AB&=\left[\begin{array}{r}{6} \\ {-2} \\ {1} \\ {6}\end{array}\right]\left[\begin{array}{r}{10} & {12 }\end{array}\right] \\ &= \left[ \begin {array}{cc} 60&72\\ -20&-24 \\ 10&12\\ 60&72\end {array} \right] . \end{align*} (b) $BA$ not defined.