Question

b2=6
b5=48
b1=?
q=?
b7=?
sn=?

Answer 1

Fie b1≠0 si q≠0;
b2=b1*q⇔b2=b1*q=6(1)
b5=b1*$q^{4}$ =48 (2)
(2):(1)⇒$\frac{48}6}$ =$\frac{b5}{b2}$ =$\frac{b1* q^{4} }{b1*q}$ 
Simplifici b1 => $\frac{ q^{4} }{q}$ =$\frac{48}{6}$=<=> $q^{3}$ =8<=> $q^{3}$ =$2^{3}$ <=> q=2
Din rel (1)=>b1=$\frac{6}{q}$ =6/2=3

b7=b1*$q^{6}$ =3*64=192
Sn=b1+b2+...+bn= b1*($\frac{ q^{n}-1 }{q-1}$) =3*$\frac{ (2^{n}-1) }{2-1}$ =3*(2^n-1)