Question

Caucular a soma da p.a (5.8.11...71)

Answer 1

$> \: resolucao \\ \\ \geqslant \: progressao \: \: aritmetica \\ \\ r = a2 - a1 \\ r = 8 - 5 \\ r = 3 \\ \\ an = a1 + (n - 1)r \\ 71 = 5 + (n - 1)3 \\ 71 = 5 + 3n - 3 \\ 71 = 2 + 3n \\ 71 - 2 = 3n \\ 69 = 3n \\ n = \frac{69}{3} \\ n = 23 \\ \\ = = = = = = = = = = = = = = = = = = \\ \\ \\ > \: soma \: dos \: termos \: da \: pa \\ \\ sn = \frac{(a1 + an)n}{2} \\ \\ sn = \frac{(5 + 71)23}{2} \\ \\ sn = \frac{76 \times 23}{2} \\ \\ sn = 38 \times 23 \\ \\ sn = 874 \\ \\ \\ \geqslant \leqslant \geqslant \leqslant \geqslant \leqslant \geqslant \leqslant \geqslant \leqslant \geqslant \geqslant$