Question

18．已知二元一次方程组$\left\{\begin{array}{l}{ax+by=13}\\{（a+b）x-ay=9}\end{array}$的解为$\left\{\begin{array}{l}{x=3}\\{y=2}\end{array}$  求a，b的值．

Answer 1

分析 把x与y的值代入方程组计算即可求出a与b的值．

解答 解：把$\left\{\begin{array}{l}{x=3}\\{y=2}\end{array}\right.$代入方程组得：$\left\{\begin{array}{l}{3a+2b=13①}\\{3a+3b-2a=9②}\end{array}\right.$，
解得：$\left\{\begin{array}{l}{a=2}\\{b=\frac{7}{3}}\end{array}\right.$．

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成立的未知数的值．