a) pt\( \Leftrightarrow \left( {1 + 2i} \right)x = - 7 + 3i + 4 - 5i\) \( \Leftrightarrow \left( {1 + 2i} \right)x = - 3 - 2i\)\( \Leftrightarrow x = - \dfrac{{3 + 2i}}{{1 + 2i}}\) \( = - \dfrac{{7 - 4i}}{5} = - \dfrac{7}{5} + \dfrac{4}{5}i\)
b) pt\( \Leftrightarrow \left( {3 + 2i - 6i} \right)x = \left( {1 - 2i} \right)x - \left( {1 - 2i} \right)\left( {1 + 5i} \right)\) \( \Leftrightarrow \left( {3 - 4i - 1 + 2i} \right)x = - \left( {1 - 2i + 5i + 10} \right)\)
\( \Leftrightarrow \left( {2 - 2i} \right)x = - \left( {11 + 3i} \right)\)\( \Leftrightarrow x = - \dfrac{{11 + 3i}}{{2\left( {1 - i} \right)}} = - 2 - \dfrac{7}{2}i\)
