Question

determine a soma dos termos de cada PA 3,11,19...115​

Answer 1

Resposta:

Dados:

a1=3

r=8

an= a1 + (n-1). r

115= 3 + (n-1) . 8

115= 3 + 8n-8

115-3+8= 8n

120= 8n

n= 120/8

n= 15

Sn= n( a1+ an) / 2

Sn= 15.(3+115) / 2

Sn= 15. 118/ 2

Sn= 1770/2

Sn= 885