Odpowiedź:
Szczegółowe wyjaśnienie:
[tex]a_n=a_1*q^{n-1}[/tex]
a₂=a₁*q¹=2
a₇=a₁*q⁶=-64
[tex]\left \{ {{a_1=\frac{2}{q} } \atop {a_1*q^6=-64}} \right. \\\left \{ {{a_1=\frac{2}{q} } \atop {\frac{2}{q}*q^6=-64 }} \right. \\\left \{ {{a_1=\frac{2}{q} } \atop {2q^5=-64}} \right.\\\left \{ {{a_1=\frac{2}{q} } \atop {q^5=-32} \right. \\\left \{ {{q=-2} \atop {a_1=-1}} \right.[/tex]
n=8
[tex]S_n=a_1\frac{1-q^n}{1-q} \\S_8=-1*\frac{1-(-2)^8}{1-(-2)} =-1*\frac{1-256}{3} =\frac{255}{3} =85[/tex]
