Förberedande kurs i matematik

\displaystyle \displaystyle (1+2i)\left( 2-\frac{i}{4} \right) = 1\cdot 2 - 1 \cdot \frac{i}{4}+2i\cdot 2- 2i\cdot \frac{i}{4}=

\displaystyle \displaystyle = 2-\frac{i}{4}+4i+\frac{1}{2} = \frac{5}{2} + \frac{15 i} {4}