Question

9．甲數(shù)為x，乙數(shù)為y，甲、乙兩數(shù)之和為15，甲數(shù)比乙數(shù)大3．根據(jù)題意可列方程組$\left\{\begin{array}{l}{x+y=15①}\\{x-y=3②}\end{array}\right.$．

Answer 1

分析 首先根據(jù)題意，可得：$\left\{\begin{array}{l}{x+y=15①}\\{x-y=3②}\end{array}\right.$，然后應(yīng)用消元法，求出方程組的解是多少即可．

解答 解：甲數(shù)為x，乙數(shù)為y，甲、乙兩數(shù)之和為15，甲數(shù)比乙數(shù)大3．根據(jù)題意可列方程組$\left\{\begin{array}{l}{x+y=15①}\\{x-y=3②}\end{array}\right.$．
①+②，可得：2x=18，
解得：x=9，
所以y=15-9=6，
所以甲數(shù)是9，乙數(shù)是6．
故答案為：$\left\{\begin{array}{l}{x+y=15①}\\{x-y=3②}\end{array}\right.$．

點評 此題主要考查了二元一次方程組的求解方法，要熟練掌握，注意代入消元法和加減消元法的應(yīng)用．