Question

14．方程组$\left\{{\begin{array}{l}{x-y=1}\\{2x+y=5}\end{array}}\right.$的解是（　　）

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

Answer 1

分析 方程组利用加减消元法求出解即可．

解答 解：$\left\{\begin{array}{l}{x-y=1①}\\{2x+y=5②}\end{array}\right.$，
①+②得：3x=6，
解得：x=2，
把x=2代入①得：y=1，
则方程组的解为$\left\{\begin{array}{l}{x=2}\\{y=1}\end{array}\right.$，
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．