ГДЗ по алгебре 7 класс Макарычев ФГОС Задание 1098

\[\boxed{\text{1098.}\text{\ }еуроки - ответы\ на\ пятёрку}\]

\[\textbf{а)}\ \left\{ \begin{matrix} 2x + 11y = 15 \\ 10x - 11y = 9 \\ \end{matrix} \right.\ ( + )\]

\[\left\{ \begin{matrix} 12x = 24 \rightarrow x = 2 \\ 10x - 11y = 9\ \ \ \ \ \ \\ \end{matrix} \right.\ \]

\[- 11y = 9 - 20\]

\[- 11y = - 11\]

\[y = 1\]

\[Ответ:(2;1).\]

\[\textbf{б)}\ \left\{ \begin{matrix} 8x - 17y = 4 \\ - 8x + 15y = 4 \\ \end{matrix} \right.\ ( + )\]

\[\left\{ \begin{matrix} - 2y = 8 \rightarrow y = - 4 \\ - 8x - 15 \cdot 4 = 4\ \ \ \ \\ \end{matrix} \right.\ \]

\[- 8x = 64\]

\[x = - 8\]

\[Ответ:( - 8;\ - 4).\]

\[\textbf{в)}\ \left\{ \begin{matrix} 4x - 7y = 30\ \ \ | \cdot ( - 1) \\ 4x - 5y = 90\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \\ \end{matrix} \right.\ \]

\[\left\{ \begin{matrix} - 4x + 7y = - 30 \\ 4x - 5y = 90\ \ \ \ \\ \end{matrix} \right.\ ( + )\]

\[\left\{ \begin{matrix} 2y = 60 \rightarrow y = 30 \\ 4x - 5 \cdot 30 = 90\ \ \ \\ \end{matrix} \right.\ \]

\[4x = 240\]

\[x = 60\]

\[Ответ:(60;30).\]

\[\textbf{г)}\left\{ \begin{matrix} 13x - 8y = 28\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \\ 11x - 8y = 24\ \ | \cdot ( - 1) \\ \end{matrix} \right.\ \]

\[\left\{ \begin{matrix} 13x - 8y = 28\ \ \ \ \ \\ - 11x + 8y = - 24 \\ \end{matrix} \right.\ ( + )\]

\[\left\{ \begin{matrix} 2x = 4 \rightarrow x = 2 \\ 13 \cdot 2 - 8y = 28 \\ \end{matrix} \right.\ \]

\[- 8y = 2\]

\[y = - \frac{1}{4} = - 0,25\]

\[Ответ:(2;\ - 0,25).\]