《2025年时习之暑假衔接七年级数学人教版》

解方程(组)：
(1)$\left\{\begin{array}{l} x+y= 22,\\ 2x+y= 40;\end{array} \right. $
(2)$\left\{\begin{array}{l} 4x-3y= 5,\\ 4x+6y= 14;\end{array} \right. $
(3)$\left\{\begin{array}{l} 3x+4y= 16,\\ 5x-6y= 33;\end{array} \right. $
(4)$\left\{\begin{array}{l} \frac {x}{2}+\frac {y}{3}= 2,\\ 4(x-y-1)= 3(1-y)-2;\end{array} \right. $
(5)$4x^{2}-24= 25;$
(6)$64x^{3}+27= 0.$

答案：
(1)$\left\{\begin{array}{l} x=18,\\ y=4.\end{array}\right. $
(2)$\left\{\begin{array}{l} x=2,\\ y=1.\end{array}\right. $
(3)$\left\{\begin{array}{l} x=6,\\ y=-\frac {1}{2}.\end{array}\right. $
(4)$\left\{\begin{array}{l} x=2,\\ y=3.\end{array}\right. $
(5)$x=\frac {7}{2}$或$x=-\frac {7}{2}$.
(6)$x=-\frac {3}{4}.$

1. 下列方程组中,是二元一次方程组的是( )

A.$\left\{\begin{array}{l} x-y= 1,\\ xy= 2\end{array} \right. $
B.$\left\{\begin{array}{l} 4x-y= 1,\\ y= 2x+3\end{array} \right. $
C.$\left\{\begin{array}{l} x^{2}-x-2= 0,\\ y= x+1\end{array} \right. $
D.$\left\{\begin{array}{l} \frac {1}{x}-1= y,\\ 3x+y= 0\end{array} \right. $

答案： B

2. 已知$\left\{\begin{array}{l} x= 1,\\ y= -1\end{array} \right. 是方程2x-ay= 3$的一组解,那么a的值为( )

A.1
B.3
C.-3
D.-15

答案： A

3. 已知$\left\{\begin{array}{l} x= -1,\\ y= 2\end{array} \right. 是二元一次方程组\left\{\begin{array}{l} 3x+2y= m,\\ nx-y= 1\end{array} \right. $的解,则$m-n$的值是( )

A.1
B.2
C.3
D.4

答案： D