Question

8．方程組$\left\{\begin{array}{l}{ax-by=1}\\{bx+ay=7}\end{array}\right.$的解是$\left\{\begin{array}{l}{x=1}\\{y=2}\end{array}\right.$，則（　�。�

• A． $\left\{\begin{array}{l}{a=1}\\{b=2}\end{array}\right.$
• B． $\left\{\begin{array}{l}{a=3}\\{b=1}\end{array}\right.$
• C． $\left\{\begin{array}{l}{a=1}\\{b=3}\end{array}\right.$
• D． $\left\{\begin{array}{l}{a=1}\\{b=7}\end{array}\right.$

Answer 1

分析 把方程組的解代入方程組，得到關(guān)于a，b的方程組，解方程組即可．

解答 解：把$\left\{\begin{array}{l}{x=1}\\{y=2}\end{array}\right.$代入程組$\left\{\begin{array}{l}{ax-by=1}\\{bx+ay=7}\end{array}\right.$得；
$\left\{\begin{array}{l}{a-2b=1}\\{b+2a=7}\end{array}\right.$，
解得：$\left\{\begin{array}{l}{a=3}\\{b=1}\end{array}\right.$，
故選：B．

點評 本題考查了二元一次方程組的解，解決本題的關(guān)鍵是解二元一次方程組．