{y=x-1
{5x+2y=16
5x+2 (x-1)=16
5x+2x-2=16
7x=16+2
7x=18:7
x=2 4/7
y=2 4/7-1
y=1 4/7
{x=2-y
{3x-2y=11
3 (2-y)-2y=11
6-3y-2y=11
-5y=11-6
-5y=5:(-5)
y=-1
x=2-(-1)
x=3
{y-2x=1
{6x-y=7
y=1+2x
6x-(1+2x)=7
6x-1-2x=7
4x=7+1
4x=8:4
x=2
y-2×2=1
y=1+4
y=5
{7x-3y=13
{x-2y=5
x=5+2y
7 (5+2y)-3y=13
35+14y-3y=13
11y=13-35
11y=-22:11
y=-2
x-2×(-2)=5
x=5-4
x=1
{x+y=6
{3x-5y=2
x=6 - y
3 (6-y)-5y=2
18-3y-5y=2
-8y=2-18
-8y=-16:(-8)
y=2
x+2=6
x=6-2
x=4
{4x-y=11
{6x-2y=13
-y=11-4x:-(1)
y=-11+4x
6x-2 (-11+4x)=13
6x+22-8x=13
-2x=13-22
-2x=-9:(-2)
x=4,5
4×4,5-y=11
-y=11-18
-y=-7:(-1)
y=7
{y-x=20
{2x-15y=-1
y=20+x
2x-15 (20+x)=-1
2x-300-15x=-1
-13x=-1+300
-13x=299; (-13)
x=23
y-23=20
y=20+23
y=43
{25-x=-4y
{3x-2y=30
-x=-4y-25:(-1)
x=4y+25
3 (4y+25)-2y=30
12y+75-2y=30
10y=30-75
10y=-45:10
y=-4.5
25-x=-4 (-4,5)
-x=18-25
-x=-7:(-1)
x=7
{2x+y=12
{7x-2y=31
y=1 2-2x
7x-2 (12-2x)=31
7x-24+4x=31
11x=31+24
11x=55:11
x=5
5×2+y=12
y=12-10
y=2
{y-2x=4
{7x-y=1
y=4+2x
7x-(4+2x)=1
7x-4-2x=1
5x=1+4
5x=5:5
x=1
y-2×1=4
y=4+2
y=6
{8y-x=4
{2x-21y=2
-x=4-8y:(-1)
x=-4+8y
2 (-4+8y)-21y=2
-8+16y-21y=2
-5y=2+8
-5y=10:(-5)
y=-2
-2×8-x=4
-x=4+16
-x=20:(-1)
x=-20
{2x-y=0,5
{3x-5y=13
-y=0,5-2x:(-1)
y=-0,5+2x
3x-5 (-0,5+2x)=13
3x+2, 5-10x=13
-7x=13-2,5
-7x=10, 5:(-7)
x=-1, 5
-1, 5×2-y=0,5
-y=0,5+3
-y=3,5:(-1)
y=-3,5