Question

Resolva:
a) (-20-8i) - (-18+7i)
b) (2-3i) . (-5-4i)

Answer 1

a) Vamos somar os termos semelhantes

$(-20-8i) - (-18+7i)\\\\ -20-8i+18-7i\\\\ \boxed{-2-15i}$

b) Propriedade distributiva, onde devemos lembrar que:

$i^2=-1\\\\ (2-3i)(-5-4i)\\\\ -10-8i+15i+12i^2\\\\ -10+7i-12\\\\ \boxed{-22+7i}$