Question

19．已知$\left\{\begin{array}{l}m=1\\ n=5\end{array}\right.$是二元一次方程组$\left\{\begin{array}{l}m+2n=b\\ 2m-n=a\end{array}\right.$的解，那么（　　）

• A． $\left\{\begin{array}{l}a=7\\ b=-9\end{array}\right.$
• B． $\left\{\begin{array}{l}a=7\\ b=11\end{array}\right.$
• C． $\left\{\begin{array}{l}a=-3\\ b=-9\end{array}\right.$
• D． $\left\{\begin{array}{l}a=-3\\ b=11\end{array}\right.$

Answer 1

分析 把m与n的值代入方程组即可求出a与b的值．

解答 解：把$\left\{\begin{array}{l}m=1\\ n=5\end{array}\right.$代入方程组$\left\{\begin{array}{l}m+2n=b\\ 2m-n=a\end{array}\right.$得：$\left\{\begin{array}{l}{a=-3}\\{b=11}\end{array}\right.$，
故选D．

点评 此题考查了二元一次方程组的解，熟练掌握运算法则是解本题的关键．