Question

Qual a soma dos 10 primeiros termos da PA (1,4,7,...)?
A)28
B)290
C)145
D)12
E)140

Answer 1

$> resolucao \\ \\ \geqslant progressao \: \: aritmetica \\ \\ r = a2 - a1 \\ r = 4 - 1 \\ r = 3 \\ \\ \\ a10 = a1 + 9r \\ a10 = 1 + 9 \times 3 \\ a10 = 1 + 27 \\ a10 = 28 \\ \\ = = = = = = = = = = = = = = = = = = = \\ \\ \\ \geqslant \: soma \: dos \: termos \: da \: pa \: \\ \\ sn = \frac{(a1 + an)n}{2} \\ \\ sn = \frac{(1 + 28)10}{2} \\ \\ sn = \frac{29 \times 10}{2} \\ \\ sn = 29 \times 5 \\ \\ sn = 145 \\ \\ \\ resposta \: > \: \: letra \: ( \: \: \: c \: \: \: ) \\ \\ \geqslant \leqslant \geqslant \leqslant \geqslant \leqslant \geqslant \leqslant \geqslant \geqslant$