Respostas

2014-04-10T12:15:44-03:00
(-6,-9,-12,...,-66) n?
r= -3 a1=-6 an=-66
an= a1+(n-1).r
-66= -6+(n-1).-3
-66= -6+(-3n-3)
-66= -6-3n+3
-66= -3-3n
3n= 63
n= 63/3
n= 21