3(x+y)-4(x-y)=5
4(x+y)-3(x-y)=9
3x+3y-4x+4y=5
4x+4y-3x+3y=9
-x+7y=5
x+7y=9
x=9-7y
-(9-7y)+7y=5
-9+7y+7y=5
14y=5+9
14y=14
y=14÷14
y=1
x=9-7×1
x=2
(x;y)=(2;1)
3(x+y)-4(x-y)=5
4(x+y)-3(x-y)=9
3x+3y-4x+4y=5
4x+4y-3x+3y=9
-x+7y=5
x+7y=9
-x+7y=5
x=9-7y
-(9-7y)+7y=5
-9+7y+7y=5
14y=5+9
14y=14
y=14÷14
y=1
x=9-7×1
x=2
(x;y)=(2;1)