Respostas

2013-08-09T13:09:36-03:00
An = A1 + ( n - 1 ) * R => 48 = 20 + ( n - 1) * 7 => 48 = 20 + 7n - 7 = > 48 - 13 = 7n => 35 = 7n => n = 35/7 => n = 5
:-) :-) :-) :-) :-) :-) :-) :-)
Espero ter ajudado =)
2013-08-09T16:09:17-03:00
An=A1+(n - 1).r
48=20+(n-1).7
48=20+7n-7
48=13+7n
48-13=7n
35=7n
35/7=n
5=n