Respostas

2014-05-12T08:42:30-03:00
An=a1+(n-1)r
a13=a1+(13-1)r
39=a1+12r
39=a1+12*4
39=a1+48
a1=39-48
a1=-9
an=a1+(n-1)r
a8=a1+(8-1)r
a8=-9+7r
a8=-9+7*4=-9+28=19
a8=19




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