Question

6．解為$\left\{\begin{array}{l}{x=4}\\{y=8}\end{array}\right.$的方程組是（　�。�

• A． $\left\{\begin{array}{l}{x+y=2}\\{x-y=1}\end{array}\right.$
• B． $\left\{\begin{array}{l}{2x-y=0}\\{x+y=12}\end{array}\right.$
• C． $\left\{\begin{array}{l}{3x+2y=13}\\{x-3y=-3}\end{array}\right.$
• D． $\left\{\begin{array}{l}{3x-2y=4}\\{3x+2y=8}\end{array}\right.$

Answer 1

分析 只要把$\left\{\begin{array}{l}{x=4}\\{y=8}\end{array}\right.$代入方程組的每一個方程，看看兩邊是否相等即可．

解答 解：A、把$\left\{\begin{array}{l}{x=4}\\{y=8}\end{array}\right.$代入方程組$\left\{\begin{array}{l}{x+y=2}\\{x-y=1}\end{array}\right.$，兩個方程的左邊和右邊都不相等，故不是此方程組的解，故本選項錯誤；
B、把$\left\{\begin{array}{l}{x=4}\\{y=8}\end{array}\right.$代入方程組$\left\{\begin{array}{l}{2x-y=0}\\{x+y=12}\end{array}\right.$，兩個方程的左邊和右邊都相等，故是此方程組的解，故本選項正確；
C、把$\left\{\begin{array}{l}{x=4}\\{y=8}\end{array}\right.$代入方程組$\left\{\begin{array}{l}{3x+2y=13}\\{x-3y=-3}\end{array}\right.$，兩個方程的左邊和右邊都不相等，故不是此方程組的解，故本選項錯誤；
D、把$\left\{\begin{array}{l}{x=4}\\{y=8}\end{array}\right.$代入方程組$\left\{\begin{array}{l}{3x-2y=4}\\{3x+2y=8}\end{array}\right.$，兩個方程的左邊和右邊都不相等，故不是此方程組的解，故選項錯誤；
故選B．

點評 本題考查了二元一次方程組的解的應(yīng)用，能理解二次一次方程組的解的定義是解此題的關(guān)鍵．