1. 已知方程组 $ \{\begin{array}{l l}3x+4y=-2, \textcircled{1}\\ 3x-2y=12, \textcircled{2}\end{array} $则 $ \textcircled{1} $ $ -\textcircled{2} $得（ ）.

A.$ 6x=14 $
B.$ 6y=-14 $
C.$ 6x=10 $
D.$ 6y=-10 $

1. B

2. 用加减消元法解方程组 $ \{\begin{array}{l l}3x+4y=1 6,\\ 5x-6y=3 3,\end{array} $如果先消去 x，下列变形正确的是（ ）.

A.$ \{\begin{array}{l l}9 x+1 2 y=4 8,\\ 1 0 x-1 2 y=6 6\end{array} $
B.$ \{\begin{array}{l l}9 x+1 2 y=1 6,\\ 1 0 x-1 2 y=3 3\end{array} $
C.$ \{\begin{array}{l l}1 5 x+2 0 y=1 6,\\ 1 5 x-1 8 y=3 3\end{array} $
D.$ \{\begin{array}{l l}1 5 x+2 0 y=8 0,\\ 1 5 x-1 8 y=9 9\end{array} $

2.D

3. 用加减消元法解方程组 $ \{\begin{array}{l l}3x-2y=-7,\\2x+5y=1\end{array} $时，有以下四种变形结果，其中变形结果正确的是（ ）。$ \textcircled{1} $ $ \{\begin{array}{l l}6x-4y=-7,\\6x+15y=1;\end{array} $$ \textcircled{2} $ $ \{\begin{array}{l l}15x-10y=-7,\\4x+10y=1;\end{array} $$ \textcircled{3} $ $ \{\begin{array}{l l}6x-4y=-14,\\6x+15y=3;\end{array} $$ \textcircled{4} $ $ \{\begin{array}{l l}15x-10y=-35,\\4x+10y=2.\end{array} $(A)只有 $ \textcircled{1} $和 $ \textcircled{2} $(B)只有 $ \textcircled{1} $和 $ \textcircled{3} $(C)只有 $ \textcircled{2} $和 $ \textcircled{3} $(D)只有 $ \textcircled{3} $和 $ \textcircled{4} $

3.D

4. 用加减消元法解方程组 $ \{\begin{array}{l l}3x-2y=3, \textcircled{1}\\ 4x+y=15 \textcircled{2}\end{array} $时，如果消去 y，较为简捷的方法是（ ）。

A.$ \textcircled{1} ×4-\textcircled{2} ×3 $
B.$ \textcircled{1} ×4+\textcircled{2} ×3 $
C.$ \textcircled{2} ×2-\textcircled{1} $
D.$ \textcircled{2} ×2+\textcircled{1} $

4.D

5. 用加减消元法解二元一次方程组 $ \{\begin{array}{l l}x+3 y=4, \textcircled{1} \\ 2 x-y=1 \textcircled{2}\end{array} $时，下列方法中无法消元的是（ ）.

A.$ \textcircled{1} ×2-\textcircled{2} $
B.$ \textcircled{2} ×(-3)-\textcircled{1} $
C.$ \textcircled{1} ×(-2)+\textcircled{2} $
D.$ \textcircled{1}-\textcircled{2} ×3 $

5.D