Respostas

2014-02-27T21:33:36-03:00
R =-9-(-6)=-9+6=-3
an = a1 + (n-1).r
-66 = -6 + (n-1). (-3)
-66+6=(n-1).(-3)
-60=(n-1). (-3)
-60/(-3) = n-1
20 = n - 1
20 + 1 = n
21 = n
1 5 1
2014-02-27T21:38:11-03:00
An = a1+(n-1).r
-66 = -6( n-1). -3
-66 = -6. 3n-3
-66= 18.3n 
3n = 18 + 66
3n = 84
  n= 84/3
n= 28
1 4 1