ГДЗ по алгебре 9 класс Мерзляк Задание 886

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\[b_{1} = 3;\ \ b_{2} = - 6\]

\[b_{2} = b_{1}\text{q\ \ }\]

\[q = \frac{b_{2}}{b_{1}} = - \frac{6}{3} = - 2\]

\[b_{1}^{3},\ b_{2}^{3},\ b_{3}^{3},\ b_{4}^{3} = b_{1}^{3},\ b_{1}^{3}q^{3},\ \left( b_{1}q \right)^{3},\ \]

\[\left( b_{1}q^{3} \right)^{3} = b_{1}^{3},\ b_{1}^{3}q^{3},\ b_{1}^{3q^{6}},b_{1}^{3q^{9}}\]

\[b_{1}^{3} = 3^{3} = 27\ \ \]

\[q = \frac{b_{1}³q³}{b_{1}³} = q³ = ( - 2)^{3} = - 8\ \]

\[S_{4} = \frac{27 \cdot \left( ( - 8)^{4} - 1 \right)}{- 8 - 1} =\]

\[= \frac{27 \cdot 4095}{- 9} = - 12\ 285\]

\[Ответ:\ - 12285.\]