\begin{array}{l}
\delta _{jk} A_k \\
\\
\delta _{jk} A_k = \left( {\delta _{1,1} + \delta _{1,2} + \delta _{1,3} + \delta _{2,1} + \delta _{2,2} + \delta _{2,3} + \delta _{3,1} + \delta _{3,2} + \delta _{3,3} } \right)A_k \\
\,\,\,\,\,\,\,\,\,\,\,\,\, = \left( {1 + 0 + 0 +...