Question

9．二元一次方程组$\left\{\begin{array}{l}{x+y=5}\\{x-y=1}\end{array}\right.$的解是（　　）

• A． $\left\{\begin{array}{l}{x=3}\\{y=2}\end{array}\right.$
• B． $\left\{\begin{array}{l}{x=6}\\{y=-1}\end{array}\right.$
• C． $\left\{\begin{array}{l}{x=4}\\{y=1}\end{array}\right.$
• D． $\left\{\begin{array}{l}{x=1}\\{y=0}\end{array}\right.$

Answer 1

分析 方程组利用加减消元法求出解即可．

解答 解：$\left\{\begin{array}{l}{x+y=5①}\\{x-y=1②}\end{array}\right.$，
①+②得：2x=6，即x=3，
①-②得：2y=4，即y=2，
则方程组的解为$\left\{\begin{array}{l}{x=3}\\{y=2}\end{array}\right.$．
故选A

点评 此题考查了解二元一次方程组，利用了消元的思想，消元的方法有：代入消元法与加减消元法．