《2025年启航新课堂八年级数学上册北师大版》

例1 解下列方程组：
(1)$\begin{cases}x - 2y = 4,\\5x - 3y = -1;\end{cases} $$\left\{\begin{array}{l} x=-2,\\ y=-3;\end{array}\right. $
(2)$\begin{cases}5x + 4y = 13,\\7x + 16y = 26.\end{cases} $$\left\{\begin{array}{l} x=2,\\ y=\frac {3}{4}.\end{array}\right. $

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

1.用代入消元法解方程组$\begin{cases}3x + 4y = 2\textcircled{1},\\2x - y = 5\textcircled{2},\end{cases} $使得代入后化简比较容易的变形是 (D)
A.由$\textcircled{1}$,得$x= \frac{2 - 4y}{3}$
B.由$\textcircled{1}$,得$y= \frac{2 - 3x}{4}$
C.由$\textcircled{2}$,得$x= \frac{y + 5}{2}$
D.由$\textcircled{2}$,得$y = 2x - 5$

答案： D