Question

16．下列是方程組$\left\{\begin{array}{l}x+2y=5\\ 2x-y=-5\end{array}$的解的是（　�。�

• A． $\left\{\begin{array}{l}x=0\\ y=0\end{array}$
• B． $\left\{\begin{array}{l}x=-5\\ y=0\end{array}$
• C． $\left\{\begin{array}{l}x=3\\ y=1\end{array}$
• D． $\left\{\begin{array}{l}x=-1\\ y=3\end{array}$

Answer 1

分析 方程組利用加減消元法求出解即可．

解答 解：$\left\{\begin{array}{l}{x+2y=5①}\\{2x-y=-5②}\end{array}\right.$，
①+②×2得：5x=-5，即x=-1，
把x=-1代入①得：y=3，
則方程組的解為$\left\{\begin{array}{l}{x=-1}\\{y=3}\end{array}\right.$，
故選D

點評 此題考查了解二元一次方程組，利用了消元的思想，消元的方法有：代入消元法與加減消元法．