Zadanie 1.
[tex]a_n < 0\\n^2-8n-9 < 0\\\Delta=(-8)^2-4*1*(-9)=64+36=100\\\sqrt\Delta=10\\n_1=\frac{8-10}{2}=-1\\n_2=\frac{8+10}{2}=9\\n\in(-1,9)\qquad\text{ale }n\in\mathbb{N}_+\\n\in\{1,2,3,4,5,6,7,8\}[/tex]
Odp: A
Zadanie 2.
[tex]a_6=1\frac{1}{2}=\frac{3}{2}\\a_4*a_5*a_6*a_7*_8=\frac{a_6}{q^2}*\frac{a_6}{q}*a_6*a_6q*a_6q^2=a_6^5=(\frac{3}{2})^5=\frac{243}{32}[/tex]
Odp: C