Đáp án: ${x = \dfrac{{ - 119}}{2};y = 199;z = \dfrac{{ - 497}}{2}}$
Giải thích các bước giải:
$\begin{array}{l}
11)Đặt:\\
\dfrac{{x + 9}}{{ - 1}} = \dfrac{{y - 98}}{2} = \dfrac{{z + 97}}{{ - 3}} = k\\
\Rightarrow \left\{ \begin{array}{l}
x + 9 = - 1.k\\
y - 98 = 2k\\
z + 97 = - 3.k
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
x = - k - 9\\
y = 2k + 98\\
z = - 3k - 97
\end{array} \right.\\
Do:x - y + z = 99\\
\Rightarrow - k - 9 - \left( {2k + 98} \right) - 3k - 97 = 99\\
\Rightarrow - 6k - 204 = 99\\
\Rightarrow 6k = 303\\
\Rightarrow k = \dfrac{{101}}{2}\\
\Rightarrow \left\{ \begin{array}{l}
x = - k - 9 = \dfrac{{ - 119}}{2}\\
y = 2k + 98 = 199\\
z = - 3k - 97 = \dfrac{{ - 497}}{2}
\end{array} \right.
\end{array}$
