q= b5/b4= 1/64:1/16= 1/64*16= 1/4
b4= b1*q³
1/16= b1*1/64
b1=4
S4= b1*(1-q⁴)/(1-q)= 4*(1-1/256)/(1-1/4)= 4*(255/256)/(3/4)= 4*(255/256)*(4/3)= 85/16= 5 5/16
q= b5/b4= 1/64:1/16= 1/64*16= 1/4
b4= b1*q³
1/16= b1*1/64
b1=4
S4= b1*(1-q⁴)/(1-q)= 4*(1-1/256)/(1-1/4)= 4*(255/256)/(3/4)= 4*(255/256)*(4/3)= 85/16= 5 5/16