Question

Determine a soma dos múltiplos de 10,compreendidos entre 12 e 129

Answer 1

$> \: resolucao \\ \\ \geqslant \: progressao \: \: aritmetica \\ \\ an = a1 + (n - 1)r \\ 120 = 20 + (n - 1)10 \\ 120 = 20 + 10n - 10 \\ 120 = 10 + 10n \\ 120 - 10 = 10n \\ 110 = 10n \\ n = \frac{110}{10} \\ n = 11 \\ \\ = = = = = = = = = = = = = = = = = \\ \\ sn = \frac{(a1 + an)n}{2} \\ \\ sn = \frac{(20 + 120)11}{2} \\ \\ sn = \frac{140 \times 11}{2} \\ \\ sn = 70 \times 11 \\ \\ sn = 770 \\ \\ \\ \leqslant \geqslant \leqslant \geqslant \leqslant \geqslant \leqslant \geqslant \leqslant \geqslant \leqslant \geqslant$