a) Ta có:
\(\left( {2 + 4i} \right)\left( {3 - 5i} \right) + 7\left( {4 - 3i} \right)\) \( = 6 + 12i - 10i + 20 + 28 - 21i\) \( = 54 - 19i\)
b) Ta có:
\({\left( {1 - 2i} \right)^2} - \left( {2 - 3i} \right)\left( {3 + 2i} \right)\) \( = 1 - 4i - 4 - \left( {6 - 9i + 4i + 6} \right)\) \( = - 15 + i\).
