а)
b_(5)=b_(1)*q^4
3=b_(1)*2^4
b_(1)=3/16
b_(8)=b_(1)*q^7
b_(8)=(3/16)*2^7
b_(8)=24
б)
S_(n)=[m]\frac{b_{1}\cdot (q^{n}-1)}{q-1}[/m]
[m]5\frac{13}{16}=\frac{\frac{3}{16}\cdot (2^{n}-1)}{2-1}[/m]
[m]5\frac{93}{16}=\frac{3}{16}\cdot (2^{n}-1)[/m]
[m]31=2^{n}-1[/m]
[m]2^{n}=32[/m]
[b]n=5[/b]
9,
b_(1)=3
b_(5)=48
b_(5)=b_(1)*q^4
48=3*q^4
q^4=16
q= ± 2
b_(2)=b_(1)*q
b_(3)=b_(1)*q^2
b_(4)=b_(1)*q^3
q=-2
b_(2)=3*(-2)=-6
b_(3)=3*(-2)^2=12
b_(4)=3*(-2)^3=-24
q=2
b_(2)=3*2=6
b_(3)=3*2^2=12
b_(4)=3*2^3=24
О т в е т. -6;12;-24 или 6;12;24