Answer
$13+18i$
Work Step by Step
Given: $(2+5i)(4-i)$
$=2(4)+2(-i)+(5i)(4)+(5i)(-i)$
$=8-2i+20i-5i^{2}$
Since, $i^2=-1$ and $i=\sqrt{-1}$
Thus,
$=8+18i-5*-1$
$=8+18i+5$
$=13+18i$
Multivariable Calculus, 7th Edition
by Stewart, James
Published by
Brooks Cole
ISBN 10:
0-53849-787-4
ISBN 13:
978-0-53849-787-9
Appendix G - Exercises - Page A12: 3
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