Question

3．二元一次方程組$\left\{\begin{array}{l}3x+2y+1=0\\ 5x-y=7\end{array}\right.$的解是（　　）

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

Answer 1

分析 方程組整理后，利用加減消元法求出解即可．

解答 解：方程組整理得：$\left\{\begin{array}{l}{3x+2y=-1①}\\{5x-y=7②}\end{array}\right.$，
①+②×2得：13x=13，即x=1，
把x=1代入①得：y=-2，
則方程組的解為$\left\{\begin{array}{l}{x=1}\\{y=-2}\end{array}\right.$，
故選B

點(diǎn)評(píng) 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．