Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Appendix G - Complex Numbers - G Exercises: 3

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 $i=\sqrt{-1}$) $=8+18i-5*-1$ $=8+18i+5$ $=13+18i$
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