Answer
$13+18i$
Work Step by Step
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 $i=\sqrt{-1}$)
$=8+18i-5*-1$
$=8+18i+5$
$=13+18i$
Calculus 8th Edition
by Stewart, James
Published by
Cengage
ISBN 10:
1285740629
ISBN 13:
978-1-28574-062-1
Appendix G - Complex Numbers - G Exercises - Page A55: 3
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