[tex]S = \frac{b1}{1-q} \\9 = \frac{b1}{1-(-1/3)} \\9 = \frac{b1}{4/3} \\b1 = 9 * 4/3\\b1 = 12[/tex]

[tex]b2 = 12 * (-1/3) = -4[/tex]

[tex]\displaystyle\bf\\q=-\frac{1}{3} \\\\S=9\\\\\\S=\frac{b_{1} }{1-q} \\\\\\b_{1} =S\cdot(1-q)=9\cdot\bigg[1-\bigg(-\frac{1}{3} \bigg)\bigg]=9\cdot\bigg(1+\frac{1}{3} \bigg)=9\cdot\frac{4}{3} =12\\\\\\b_{2} =b_{1} \cdot q=12\cdot\bigg(-\frac{1}{3} \bigg)=-4\\\\\\Otvet: \ b_{2} =-4[/tex]