Question

19．下列各对x，y的值是方程3x-2y=7的解是（　　）

• A． $\left\{\begin{array}{l}{x=1}\\{y=2}\end{array}\right.$
• B． $\left\{\begin{array}{l}{x=3}\\{y=-1}\end{array}\right.$
• C． $\left\{\begin{array}{l}{x=-1}\\{y=-5}\end{array}\right.$
• D． $\left\{\begin{array}{l}{x=5}\\{y=-4}\end{array}\right.$

Answer 1

分析 把选项中各对x、y的值代入方程3x-2y=7，逐一验证，判断出哪对x，y的值是方程3x-2y=7的解即可．

解答 解：当$\left\{\begin{array}{l}{x=1}\\{y=2}\end{array}\right.$时，
3×1-2×2=-1≠7，
∴$\left\{\begin{array}{l}{x=1}\\{y=2}\end{array}\right.$不是方程3x-2y=7的解．

当$\left\{\begin{array}{l}{x=3}\\{y=-1}\end{array}\right.$时，
3×3-2×（-1）=11≠7，
∴$\left\{\begin{array}{l}{x=3}\\{y=-1}\end{array}\right.$不是方程3x-2y=7的解．

当$\left\{\begin{array}{l}{x=-1}\\{y=-5}\end{array}\right.$时，
3×（-1）-2×（-5）=7，
∴$\left\{\begin{array}{l}{x=-1}\\{y=-5}\end{array}\right.$是方程3x-2y=7的解．

当$\left\{\begin{array}{l}{x=5}\\{y=-4}\end{array}\right.$时，
3×5-2×（-4）=23≠7，
∴$\left\{\begin{array}{l}{x=5}\\{y=-4}\end{array}\right.$不是方程3x-2y=7的解．
故选：C．

点评 此题主要考查了二元一次方程的解，要熟练掌握，采用代入法即可．