a \left[ {\begin{array}{*{20}c} 1 & 2 \\ { 0} & { 1} \\ \end{array}} \right] + b \left[ {\begin{array}{*{20}c} 0 & 0 \\ { -1} & { 1} \\ \end{array}} \right] + c \left[ {\begin{array}{*{20}c} 0 & 2 \\ { 1} & { 1} \\ \end{array}} \right] = \left[ {\begin{array}{*{20}c} 0 & 0 \\ { 0} & { 0} \\ \end{array}} \right]