Question

5．已知$\left\{\begin{array}{l}{x=-1}\\{y=2}\end{array}\right.$是二元一次方程$\left\{\begin{array}{l}{3x+2ny=m}\\{nx-y=1-m}\end{array}\right.$的解，則n-m的值是-3．

Answer 1

分析 把x與y的值代入方程組計(jì)算求出m與n的值，即可求出n-m的值．

解答 解：把$\left\{\begin{array}{l}{x=-1}\\{y=2}\end{array}\right.$代入方程組得：$\left\{\begin{array}{l}{-3+4n=m}\\{-n-2=1-m}\end{array}\right.$，
解得：m=5，n=2，
則n-m=2-5=-3．
故答案為：-3

點(diǎn)評(píng) 此題考查了二元一次方程組的解，方程組的解即為能使方程組中兩方程都成立的未知數(shù)的值．