Respostas

2014-03-16T22:25:37-03:00
A20=a1+r*(n-1)
a20=5+4*(20-1)
a20=5+4*19
a20=81

s=(a1+a20)*n/2
s=(5+81)*20/2
s=860
2 5 2
2014-03-16T22:34:35-03:00
An = 5 + (20 - 1) .r   
a20 = 5 + 19.4
a20 = 81

Sn = (a1 +an) . n / 2 
     = 5 + 81 . 20/2 
     = 1720/2 = 860

3 5 3