Vermenigvuldigen en delen (a+bi)

Bereken

\((9+4i) \cdot (5-3i)\)

\((9+4i) \cdot (5-3i)= 45-27i +20 i-12i^2 = 45-27i +20 i+12= \color{red}{45+12}\color{blue}{-27i +20i}=\color{red}{57}\color{blue}{-7i}\)