Respostas

2014-02-24T19:41:39-03:00
A1= 20

an=90

razão => R=5

an= a1+(n-1).R

90 = 20 + (n-1).5 => n = 15 termos

soma=(a1+a15).15/2 = (20+90).15/2 = 825

2 4 2
2014-02-24T19:41:50-03:00
20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80 e 85.