Question

ache a soma dos 40 primeiros termos da P.A. (2,4,6)

Answer 1

$r=4-2\\ \boxed{r=2}\\\\ A_n=A_1+(n-1).r\\ A_{40}=2+39.2\\ A_{40}=2+78\\ \boxed{A_{40}=80}\\\\ S_n=\frac{(A_1+A_n).n}2\\ S_{40}=\frac{(2+80).40}2\\ S_{40}=82.20\\ \boxed{S_{40}=1640}$