《2025年新课程能力培养八年级数学上册北师大版》

1. 解下列三元一次方程组：
(1) $\begin{cases}x = 2y - 7 \\ 5x + 3y + z = -9 \\ 3x - 4z = -9\end{cases} $
(2) $\begin{cases}x + y = 7 \\ y + z = 8 \\ z + x = 13\end{cases} $
(3) $\begin{cases}4x - 9z = 17 \\ 3x + y + 15z = 18 \\ x + 2y + 3z = 2\end{cases} $
(4) $\begin{cases}3x - y + z = 4 \\ 2x + 3y - z = 12 \\ x + y + z = 6\end{cases} $

答案： （1）$\left\{\begin{array}{l} x=-3,\\ y=2,\\ z=0\end{array}\right. $（2）$\left\{\begin{array}{l} x=6,\\ y=1,\\ z=7\end{array}\right. $（3）$\left\{\begin{array}{l} x=5,\\ y=-2,\\ z=\frac {1}{3}\end{array}\right. $（4）$\left\{\begin{array}{l} x=2,\\ y=3,\\ z=1\end{array}\right. $