Odpowiedź :
x-3y=9
3x+y=7 /*3
x-3y=9
9x+3y=21
__________
10x=30 /:10
x=3
y=7-3x
y=7-9
y=-2
x=3
y=-2
3x+y=7 /*3
x-3y=9
9x+3y=21
__________
10x=30 /:10
x=3
y=7-3x
y=7-9
y=-2
x=3
y=-2
{x-3y=9/-3
{3x+y=7
{-3x+9y=-27
{3x-y=7
-------------
-3x-9y+3x-y=-27+7
-10y+-20
y=2
x-3*2=9
x=6+9
x=15
{3x+y=7
{-3x+9y=-27
{3x-y=7
-------------
-3x-9y+3x-y=-27+7
-10y+-20
y=2
x-3*2=9
x=6+9
x=15
{x-3y=9 I*-3
{3x+y=7
(-3x+9=27
(3x=y=7
(9y=20:9
(y=20/9
y=2.22
x+2.22=9
x=9-2.22
x=6.78
{3x+y=7
(-3x+9=27
(3x=y=7
(9y=20:9
(y=20/9
y=2.22
x+2.22=9
x=9-2.22
x=6.78