Resposta:Segue as contas abaixo na explicação
Explicação passo-a-passo:
a)a1=48,q=a2/a1--->q=12/48:12/12--->q=1/4,Sn=?
Sn=a1/1-q
Sn=48/1-1/4
Sn=48/4/4-1/4
Sn=48/3/4
Sn=48/12
Sn=4
b)a1=75,q=a2/a1--->q=15/75:15/15--->q=1/5,Sn=?
Sn=a1/1-q
Sn=75/1-1/5
Sn=75/5/5-1/5
Sn=75/4/5
Sn=75/20:5/5
Sn=15/4
c)a1=-98,q=a2/a1--->q=14/-98:14/14--->q=-1/7,Sn=?
Sn=a1/1-q
Sn=-98/1-(-1/7)
Sn=-98/1+1/7
Sn=-98/7/7+1/7
Sn=-98/8/7
Sn=-98/56:14/14
Sn=-7/4
d)a1=175,q=a2/a1--->q=-35/175:35/35--->q=-1/5,Sn=?
Sn=a1/1-q
Sn=175/1-(-1/5)
Sn=175/1+1/5
Sn=175/5/5+1/5
Sn=175/6/5
Sn=175/30:5/5
Sn=35/6
e)a1=-80,q=a2/a1--->q=-20/-80:20/20--->q=-1/4,Sn=?
Sn=a1/1-q
Sn=-80/1-(-1/4)
Sn=-80/1+1/4
Sn=-80/4/4+1/4
Sn=-80/5/4
Sn=-80/20
Sn=-4
f)a1=-648,q=a2/a1--->q=-72/-648:-72/-72--->q=1/9,Sn=?
Sn=a1/1-q
Sn=-648/1-1/9
Sn=-648/9/9-1/9
Sn=-648/8/9
Sn=-648/72
Sn=-9