a)
2x+4y=5y-1
y+5=0
--------
2x+4y-5y=-1
y=-5
--------
2x-y=-1
2x-(-5)=-1
2x+5=-1 |-5
2x=-6 |:2
x=-3
x=-3
y=-5
b)
2x-y=4
\frac{x-3}{4}=\frac{y-2}{5} |20
---------
-y=-2x+4 |(-1)
5(x-3)=4(y-2)
---------
y=2x-4
5x-15=4y-8 |+15
---------
y=2x-4
5x-4y=7
podstawiam y
5x-4(2x-4)=7
5x-8x+16=7 |-16
-3x=-9 |:(-3)
x=3
y=2x-4
y=2*3-4
y=2
x=3
y=2