# Why the dual and the canonical dual may have the same optimal solution?

For instance let be

\begin{cases} \max & 3x_1 &+2x_2 &+4x_3 & -x_4\\ &x_1 &+x_2 &-2x_3&&\le4\\ &2x_1&+3x_3&&-4x_4&\ge 5\\ &2x_1&+x_2&+3x_3&&=7\\ x_1,x_2\ge 0\\ x_4\le 0 \end{cases}

Why may the dual and the canonical dual have the same optimal solution?