Question

21.(Cescem) O produto (5 + 7i)(3 - 2i) vale:
a) 1 + lli
b) 1+31i
c) 29 + 1li
e) 29 + 31i
d) 29 - 11

Answer 1

$\LARGE\displaystyle{}\left(5 + 7i\right) \times \left(3 - 2i\right) \\\\ \LARGE\displaystyle{}5 \times 3 - 5 \times 2i + 7i \times 3 - 7i \times 2i \\ \\ \LARGE\displaystyle{}15 - 10i + 21i - {14i}^{2} \\ \\ \LARGE\displaystyle{}15 - 10i + 21i \times \left( - 1\right) \\ \\ \LARGE\displaystyle{}15 - 10i + 21i + 14 \\ \LARGE\displaystyle{}29 + 11i$

Então concluímos que:

$\LARGE\displaystyle\text{ \begin{gathered} \underline{\boxed{\boldsymbol{ Alternativa~D }}}\end{gathered} }$

$\LARGE\displaystyle\text{ \begin{gathered} \underline{\boxed{\boldsymbol{{ \red{Bons}} \blue{\:Estudos}}}}\end{gathered} }$