Question

Dada a PA (1,4,7,10...) calcule a soma dos 35 primeiros termos

Answer 1

$\\ a1 = 1 \\ r = 3 \\ n = 35 \\ an = ? \\ Sn = ?$

$\\ an = a1 + (n-1).r \\ a35 = 1 + (35 - 1).3 \\ a35 = 1 + 34.3 \\ a35 = 1 + 102 \\ a35 = 103$

$\\ Sn = \frac{(a1 + an).n}{2} \\ S35 = \frac{(1 + 103).35}{2} \\ S35 = \frac{104.35}{2} \\ Sn = 52.35 \\ Sn = 1820$