Question

Calcule a soma das 15 primeiros termos faz PA (1,4,7,10,13,16. )

Answer 1

$> resolucao \\ \\ \geqslant progressao \: \: aritmetica \\ \\ r = a2 - a1 \\ r = 4 - 1 \\ r = 3 \\ \\ \\ a15 = a1 + 14r \\ a15 = 1 + 14 \times 3 \\ a15 = 1 + 42 \\ a15 = 43 \\ \\ \\ \geqslant \: a \: soma \: dos \: 15 \: temos \: da \: pa \\ \\ \\ sn = \frac{(a1 + an)n}{2} \\ \\ sn = \frac{(1 + 43)15}{2} \\ \\ sn = \frac{44 \times 15}{2} \\ \\ sn = 22 \times 15 \\ \\ sn = 330 \\ \\ \\ \geqslant \leqslant \geqslant \leqslant \geqslant \leqslant \geqslant \leqslant \geqslant \leqslant \geqslant \geqslant$