Calculus 8th Edition

$13+18i$
We distribute: $(2+5i)(4-i)$ $=2(4)+2(-i)+(5i)(4)+(5i)(-i)$ $=8-2i+20i-5i^{2}$ We use the fact that $i^2=-1$ (because $i=\sqrt{-1}$) $=8+18i-5*-1$ $=8+18i+5$ $=13+18i$