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2.已知关于$x,y$的二元一次方程组$\begin{cases}ax - y = 4, \\ 3x + by = 4\end{cases}$的解是$\begin{cases}x = 2, \\ y = -2,\end{cases}$则$a+b$的值是（ ）.
A.1
B.2
C.$-1$
D.0
A.1
B.2
C.$-1$
D.0
答案
2.B
3.《孙子算经》是中国古代重要的数学著作，成书大约在一千五百年前，其中一道题，原文是：“今三人共车，两车空；二人共车，九人步.问人与车各几何？”意思是：现有若干人和车，若每辆车乘坐3人，则空余2辆车；若每辆车乘坐2人，则有9人步行，问人与车各多少？设有$x$人，$y$辆车，可列方程组为（
A.$\begin{cases} \dfrac{x}{3} = y + 2 \\ \dfrac{x}{2} + 9 = y \end{cases}$
B.$\begin{cases} \dfrac{x}{3} = y - 2 \\ \dfrac{x - 9}{2} = y \end{cases}$
C.$\begin{cases} \dfrac{x}{3} = y + 2 \\ \dfrac{x - 9}{2} = y \end{cases}$
D.$\begin{cases} \dfrac{x}{3} = y - 2 \\ \dfrac{x}{2} - 9 = y \end{cases}$
B
）。A.$\begin{cases} \dfrac{x}{3} = y + 2 \\ \dfrac{x}{2} + 9 = y \end{cases}$
B.$\begin{cases} \dfrac{x}{3} = y - 2 \\ \dfrac{x - 9}{2} = y \end{cases}$
C.$\begin{cases} \dfrac{x}{3} = y + 2 \\ \dfrac{x - 9}{2} = y \end{cases}$
D.$\begin{cases} \dfrac{x}{3} = y - 2 \\ \dfrac{x}{2} - 9 = y \end{cases}$
答案
3.B
4.若$a+2b=8,3a+4b=18$,则$a+b$的值为
5
.答案
4.5
5.解下列方程组.
(1) $\begin{cases}2x + 3y = 5, \\2x - 7y = 15;\end{cases}$
(2) $\begin{cases}6x - 3y = -3, \\5x - 9y = 4;\end{cases}$
(3) $\begin{cases}\dfrac{2x - 1}{5} + \dfrac{3y - 2}{4} = 0, \\\dfrac{3x - 1}{5} + \dfrac{3y + 2}{4} = 0;\end{cases}$
(4) $\begin{cases}\dfrac{x}{2} + \dfrac{y}{3} = \dfrac{1}{6}, \\2(x - 1) + 3(x - y) = 6.\end{cases}$
(1) $\begin{cases}2x + 3y = 5, \\2x - 7y = 15;\end{cases}$
(2) $\begin{cases}6x - 3y = -3, \\5x - 9y = 4;\end{cases}$
(3) $\begin{cases}\dfrac{2x - 1}{5} + \dfrac{3y - 2}{4} = 0, \\\dfrac{3x - 1}{5} + \dfrac{3y + 2}{4} = 0;\end{cases}$
(4) $\begin{cases}\dfrac{x}{2} + \dfrac{y}{3} = \dfrac{1}{6}, \\2(x - 1) + 3(x - y) = 6.\end{cases}$
答案
5.(1)$\begin{cases} x = 4 \\ y = -1 \end{cases}$
(2)$\begin{cases} x = -1 \\ y = -1 \end{cases}$
(3)$\begin{cases} x = -5 \\ y = \frac{18}{5} \end{cases}$
(4)$\begin{cases} x = 1 \\ y = -1 \end{cases}$
(2)$\begin{cases} x = -1 \\ y = -1 \end{cases}$
(3)$\begin{cases} x = -5 \\ y = \frac{18}{5} \end{cases}$
(4)$\begin{cases} x = 1 \\ y = -1 \end{cases}$
