We compute the product by distributing: u z = ( 1 + 3 i ) ( 2 − i ) = 2 − i + 6 i − 3 i 2 = 2 + 5 i + 3 = 5 + 5 i . {\displaystyle {\begin{aligned}uz&=(1+3i)(2-i)\\&=2-i+6i-3i^{2}\\&=2+5i+3\\&=5+5i.\end{aligned}}} Answer: u z = 5 + 5 i {\displaystyle \color {blue}uz=5+5i}