$\displaystyle{A = {\left[\begin{array}{ccc} -3 &1 &-3\cr 3 &5 &0 \end{array}\right]} \ \ \mbox{and} \ \ B = {\left[\begin{array}{ccc} -3 &2 &-1\cr 1 &-1 &2 \end{array}\right]}. }$