Question

加减消元法解二元一次方程组，要标准过程。

（1）｛x+y/2+x-y/2=7 4(x+y)-5(x-y)=2
（2）｛x+y=360 112％x+110％y=400

Answer 1

（1）x+y/2+x-y/2=7 ················1
4(x+y)-5(x-y)=2··················2
1式X10+2式得：
9(x+y)=72 即：x+y=8 ·············3
1式X8－2式得：
9(x-y)=54 即：x-y=6···············4
由3式－4式得：
2y=2 解得：y=1
由3式＋4式得：
2x=14 解得：x=7

（2）｛x+y=360 ···························1
112％x+110％y=400······················2
由1式X110%－2式得：
1.1x-1.12x=396-400
-0.02x=-4
解得：x=200 代入1式得：
y=160