b1=V6 b2=V18 q=b2/b1=V3
S4=b1(q^4-1)/q-1={V6(9-1)}/(v3 -1)= 8V6(V3+1)/{(V3-1)(V3+1)=8V6(V3+1)/2=4V6(V3+1)=
=4V18-4V6=12V2-4V6
b1=V6 b2=V18 q=b2/b1=V3
S4=b1(q^4-1)/q-1={V6(9-1)}/(v3 -1)= 8V6(V3+1)/{(V3-1)(V3+1)=8V6(V3+1)/2=4V6(V3+1)=
=4V18-4V6=12V2-4V6