Question

13．已知$\left\{\begin{array}{l}{x=2}\\{y=1}\end{array}\right.$和$\left\{\begin{array}{l}{x=1}\\{y=-2}\end{array}\right.$都是方程ax+y=b的解，求a與b的值．

Answer 1

分析 把x與y的兩對值代入方程計算即可求出a與b的值．

解答 解：∵$\left\{\begin{array}{l}{x=2}\\{y=1}\end{array}\right.$和$\left\{\begin{array}{l}{x=1}\\{y=-2}\end{array}\right.$都是方程ax+y=b的解，
∴$\left\{\begin{array}{l}{2a+1=b}\\{a-2=b}\end{array}\right.$，
解得：$\left\{\begin{array}{l}{a=-3}\\{b=-5}\end{array}\right.$．

點評 此題考查了二元一次方程的解，方程的解即為能使方程左右兩邊相等的未知數的值．