Question

8．方程組$\left\{\begin{array}{l}3x+y=3\\-4x-y=3\end{array}\right.$的解是（　　）

• A． $\left\{\begin{array}{l}x=0\\ y=3\end{array}\right.$
• B． $\left\{\begin{array}{l}x=0\\ y=-3\end{array}\right.$
• C． $\left\{\begin{array}{l}x=6\\ y=-15\end{array}\right.$
• D． $\left\{\begin{array}{l}x=-6\\ y=21\end{array}\right.$

Answer 1

分析 先用加減消元法求出x的值，再用代入消元法求出y的值即可．

解答 解：$\left\{\begin{array}{l}3x+y=3①\\-4x-y=3②\end{array}\right.$，①+②得，-x=6，解得x=-6，
把x=-6代入①得，-18+y=3，解得y=21．
所以方程組的$\left\{\begin{array}{l}x=-6\\ y=21\end{array}\right.$．
故選D．

點評 本題考查的是解二元一次方程組，熟知解二元一次方程組的加減消元法和代入消元法是解答此題的關(guān)鍵．