Question

4．方程组$\left\{\begin{array}{l}{3x+y=7}\\{x-y=5}\end{array}\right.$的解是$\left\{\begin{array}{l}{x=3}\\{y=-2}\end{array}\right.$．

Answer 1

分析 方程组利用加减消元法求出解即可．

解答 解：$\left\{\begin{array}{l}{3x+y=7①}\\{x-y=5②}\end{array}\right.$，
①+②得：4x=12，即x=3，
把x=3代入①得：y=-2，
则方程组的解为$\left\{\begin{array}{l}{x=3}\\{y=-2}\end{array}\right.$．
故答案为：$\left\{\begin{array}{l}{x=3}\\{y=-2}\end{array}\right.$．

点评 此题考查了解二元一次方程组，熟练掌握运算法则是解本题的关键．