Question

15．方程组$\left\{\begin{array}{l}x+y=3\\ 2x-y=-6\end{array}\right.$的解是$\left\{\begin{array}{l}{x=-1}\\{y=4}\end{array}\right.$．

Answer 1

分析 方程组利用加减消元法求出解即可．

解答 解：$\left\{\begin{array}{l}{x+y=3①}\\{2x-y=-6②}\end{array}\right.$，
①+②得：3x=-3，
解得：x=-1，
把x=-1代入①得：y=4，
则方程组的解为$\left\{\begin{array}{l}{x=-1}\\{y=4}\end{array}\right.$，
故答案为：$\left\{\begin{array}{l}{x=-1}\\{y=4}\end{array}\right.$

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．