Question

8．已知$\left\{\begin{array}{l}{x=2}\\{y=1}\end{array}\right.$是方程组$\left\{\begin{array}{l}{ax-3y=1}\\{x+by=5}\end{array}\right.$的解，则a，b的值分别是（　　）

• A． 3，2
• B． 2，3
• C． -3，2
• D． -2，3

Answer 1

分析 把$\left\{\begin{array}{l}{x=2}\\{y=1}\end{array}\right.$代入方程组$\left\{\begin{array}{l}{ax-3y=1}\\{x+by=5}\end{array}\right.$，解方程组即可求解．

解答 解：把$\left\{\begin{array}{l}{x=2}\\{y=1}\end{array}\right.$代入方程组$\left\{\begin{array}{l}{ax-3y=1}\\{x+by=5}\end{array}\right.$，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：B．

点评 本题考查了二元一次方程组的解，解决本题的关键是利用代入法求解．