Question

9．如果$\left\{\begin{array}{l}{x=2}\\{y=-1}\end{array}\right.$是方程组$\left\{\begin{array}{l}{ax-3y=5}\\{2x+by=1}\end{array}\right.$的解，求b-a的值．

Answer 1

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

解答 解：把$\left\{\begin{array}{l}{x=2}\\{y=-1}\end{array}\right.$代入方程组$\left\{\begin{array}{l}{ax-3y=5}\\{2x+by=1}\end{array}\right.$中，
可得：$\left\{\begin{array}{l}{2a+3=5}\\{4-b=1}\end{array}\right.$，
解得：$\left\{\begin{array}{l}{a=1}\\{b=3}\end{array}\right.$，
把a=1，b=3代入b-a=3-1=2．

点评 本题考查了二元一次方程组的解，属于基础题，关键是掌握用代入法解方程组．