1)(x+y=1 /*-3
(x+3y=9
+ (-3x-3y=-3
-2x=6
x=-3
-3+y=1
y=4 (-3; 4)
2)(x+y=1 x=1-y
1-y+3y=9
2y=8
y=4
x=1-y
x=1-4
x=-3 (-3; 4)
1)(x+y=1 /*-3
(x+3y=9
+ (-3x-3y=-3
(x+3y=9
-2x=6
x=-3
-3+y=1
y=4 (-3; 4)
2)(x+y=1 x=1-y
(x+3y=9
1-y+3y=9
2y=8
y=4
x=1-y
x=1-4
x=-3 (-3; 4)