Question

Геометриялық прогрессия q=2, S7=635 B6=???

Answer 1

q=2 
S7=635
Sn=b1(q^7-1)/(q-1)
b1(2^7-1)/(2-1)=635
b1=635/127=5
bn=b1q^(n-1)
b6=5*2^5=5*32=160

Answer 2

Sn= b1*(1-q^n)/1-q
bn=b1*q^n-1
635=b1*(1-q^7)/1-2
635=b1*(1-128)/1-2 ⇒ b1=5
b6= 5*2^6-1=5*2^5=160