Question

19．若 $\left\{\begin{array}{l}x=2\\ y=1\end{array}\right.$是方程组$\left\{\begin{array}{l}ax-3y=1\\ x+by=5\end{array}\right.$的解，则a、b值为（　　）

• A． $\left\{\begin{array}{l}a=2\\ b=3.\end{array}\right.$
• B． $\left\{\begin{array}{l}a=-2\\ b=3.\end{array}\right.$
• C． $\left\{\begin{array}{l}a=2\\ b=-3.\end{array}\right.$
• D． $\left\{\begin{array}{l}a=-2\\ b=-3.\end{array}\right.$

Answer 1

分析 把x与y的值代入方程组求出a与b的值即可．

解答 解：把$\left\{\begin{array}{l}{x=2}\\{y=1}\end{array}\right.$代入方程组得：$\left\{\begin{array}{l}{2a-3=1}\\{2+b=5}\end{array}\right.$，
解得：$\left\{\begin{array}{l}{a=2}\\{b=3}\end{array}\right.$，
故选A

点评 此题考查了二元一次方程组的解，方程组的解即为能使方程组中两方程都成立的未知数的值．