Answer
$21 - 20i$
Work Step by Step
RECALL:
(1) $(a-b)^2 = a^2 - 2ab + b^2$
(2) $i^2=-1$
Use rule (1) above with $a=5$ and $b=2i$ to obtain:
$=5^2 - 2(5)(2i) + (2i)^2
\\=25 - 20i + 4i^2$
Use rule (2) above to obtain:
$=25 - 20i + 4(-1)
\\=25 - 20i+(-4)
\\=21 - 20i$
