Question

observe PA(15,20,..........,135) determine a soma dos termos dessa PA. Fórmulas:An=a1+(n-1)r e Sn=n/2(a1+An)​

Answer 1

$> resolucao \\ \\ \geqslant progressao \: aritmetica \\ \\ r = a2 - a1 \\ r = 20 - 15 \\ r = 5 \\ \\ an = a1 + (n - 1)r \\ 135 = 15 + (n - 1)5 \\ 135 = 15 + 5n - 5 \\ 135 = 10 + 5n \\ 135 - 10 = 5n \\ 125 = 5n \\ n = \frac{125}{5} \\ n = 25 \\ \\ = = = = = = = = = = = = = = = = = = \\ \\ \geqslant \: soma \: dos \: termos \: da \: pa \\ \\ sn = \frac{(a1 + an)n}{2} \\ \\ sn = \frac{(15 + 135)25}{2} \\ \\ sn = \frac{150 \times 25}{2} \\ \\ sn = 75 \times 25 \\ \\ sn = 1875 \\ \\ > < > < > < > < > < > < > > < > < >$