(1)b1=S1=2/3(b1-1)
b1=-2
S2=-2+b2=2/3(b2-1)
b2=4
d=a3-a2=b2-b1=6
a1=a2-d=-8
an=a1+(n-1)d=6n-14
(2)S(n-1)=2/3[b(n-1)-1]
bn=Sn-S(n-1)=2/3(bn-1)-2/3[b(n-1)-1]
bn/b(n-1)=-2
Sn=b1*(1-q^n)/(1-q)=2/3*(-2)^n-2/3
(1)b1=S1=2/3(b1-1)
b1=-2
S2=-2+b2=2/3(b2-1)
b2=4
d=a3-a2=b2-b1=6
a1=a2-d=-8
an=a1+(n-1)d=6n-14
(2)S(n-1)=2/3[b(n-1)-1]
bn=Sn-S(n-1)=2/3(bn-1)-2/3[b(n-1)-1]
bn/b(n-1)=-2
Sn=b1*(1-q^n)/(1-q)=2/3*(-2)^n-2/3