Đáp án:
Giải thích các bước giải:
\(\begin{array}{l}
a.\left\{ \begin{array}{l}
z = 3x + 5y - 2\\
y = 3z - 3 + 9\\
x = 4z - 4 + 12
\end{array} \right. \to \left\{ \begin{array}{l}
z = 3.\left( {4z + 8} \right) + 5\left( {3z + 6} \right) - 2\\
y = 3z + 6\\
x = 4z + 8
\end{array} \right.\\
\to \left\{ \begin{array}{l}
z = - 2\\
y = 0\\
x = 0
\end{array} \right.\\
e.\left\{ \begin{array}{l}
x - 7 = y\\
{x^3} - \left( {{x^3} - 21{x^2} + 147x - 343} \right) = 133
\end{array} \right.\\
\to \left\{ \begin{array}{l}
y = x - 7\\
\left[ \begin{array}{l}
x = 5\\
x = 2
\end{array} \right. \to \left[ \begin{array}{l}
y = - 2\\
y = - 5
\end{array} \right.
\end{array} \right.
\end{array}\)
