Question

2x-y=11
5x-4y=8

x-y=-7
3x+2y=-6

Answer 1

2x-y=11
5x-4y=8

y=-11+2x
5x-4(-11+2x)=8

y=-11+2x
5x+44-8x=8

y=-11+2x
-3x=-36     /:(-3)

y=-11+2x
x=12

y=-11+24
x=12

y=13
x=12

spr: 2x-y=11
2*12-13=24-13=11

x-y=-7
3x+2y=-6

x=-7+y
3(-7+y)+2y=-6

x=-7+y
-21+3y+2y=-6

x=-7+y
5y=15   /:5

x=-7+y
y=3

x=-7+3
y=3

x=-4
y=3

spr:x-y=-7
-4-3=-7

Answer 2

a)
{2x+y=11
{5x-4y=8

y = 11-2x
5x-4(11-2x) = 8

y = 11-2x
8x+5x=44+8

y = 11-2x
13x = 8+44
y = 11-2x
13x = 52  |:13
y = 11-2x
x = 52/13 = 4
y = 11-2*4=11-8=3

x=4 

Czyli :
y = 3
x  = 4
b)
5*4-4y=8

20-4y=8

4y=20-8

4y=12

y=3 

Czyli:

x=4

y=3

c)
{3x+2y=1
{5x-y=6/*2 

3x+2y=1

10x-2y=12

3x+10x=1+12
13x=13
x=1 

3*1+2y=1
3+2y=1
2y=1-3
2y=-2

y=-1 

Czyli:
x=1

y=-1