Question

解方程{3(x+y)-4(x-y)=-9① 2分之x+y+6分之x-y=1②

Answer 1

3(x+y)-4(x-y)=-9
3x+3y-4x+4y=-9
x-7y=9①
2分之x+y+6分之x-y=1
3(x+y)+(x-y)=6
4x+2y=6
2x+y=3②

②-①*2得
15y=-15
y=-1
代入①得
x+7=9
x=2

解得
x=2
y=-1

Answer 2

令 x+y=a
x-y=b
3a-4b=-9 --------------------------------①
a/2+b/6=1 --------- 3a+b=6 ----------②
∴ ②-① 得：5b=15 b=3
∴a=1
∴ x+y=1
x-y=3
解得：x=2 y=-1