B4-b2=2,b7-b5=54, b1=?, s5=?
b4=b2.q², b7=b5.q²
b2.q²-b2=2
b5.q²-b5=54
b2(q²-1)=2
b5(g²-1)=54, b5=b2.q³
b2.q³(q²-1)=54
(b2.q³(q²-1))/b2(q²-1)=54/2
q³=27, q=∛27, q=3
b1.q³-b1.q=2
27b1-3b1=2
24b1=2, b1=1/12
b2=1/4,b3=3/4,b4=9/4, b5=27/4,b6=81/4, b7=243/4
9/4-1/4=8/4=2
243/4-27/4=216/4=54
s5=b1.(qˇ5 -1)/(q-1)
s5=(1/12)(3ˇ5 -1)/(3-1)
s5=(1/12)(242)/2=(1/12).121=121/12
1/12+1/4+3/4+9/4+27/4=1/12+40/4=1/12+10=1/12+120/12=121/12
Otvet: b1=1/12, s5=121/12