Question

4．二元一次方程组$\left\{\begin{array}{l}{x+y=5}\\{2x-y=7}\end{array}\right.$的解为（　　）

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

Answer 1

分析 方程组利用加减消元法求出解即可．

解答 解：$\left\{\begin{array}{l}{x+y=5①}\\{2x-y=7②}\end{array}\right.$，
①+②得：3x=12，
解得：x=4，
把x=4代入①得：y=1，
则方程组的解为$\left\{\begin{array}{l}{x=4}\\{y=1}\end{array}\right.$，
故选C

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．