Question

3．已知關(guān)于x，y的二元一次方程組$\left\{\begin{array}{l}{x+my=4}\\{nx+3y=2}\end{array}\right.$的解是$\left\{\begin{array}{l}{x=1}\\{y=-3}\end{array}\right.$，求m+n的值．

Answer 1

分析 先把$\left\{\begin{array}{l}{x=1}\\{y=-3}\end{array}\right.$代入方程，求得m、n的值，最后把m、n的值代入所求代數(shù)式計(jì)算即可．

解答 解：把$\left\{\begin{array}{l}{x=1}\\{y=-3}\end{array}\right.$代入方程組$\left\{\begin{array}{l}{x+my=4}\\{nx+3y=2}\end{array}\right.$得$\left\{\begin{array}{l}{1-3m=4}\\{n-9=2}\end{array}\right.$，
解得m=-1，n=11，
所以m+n=10．

點(diǎn)評(píng) 本題考查了二元一次方程的解，掌握方程組的解適合每一個(gè)方程是解決問(wèn)題的關(guān)鍵．