2x-y=15
y=0 to 2x-0=15 2x=15 |:2 x=7,5
y=1 to 2x-1=15 2x=15+1 2x=16 |:2 x=8
Pary to (7,5;0), (8;1)
x+y=9
x=0 to 0+y=9 y=9
x=2 to 2+y=9 y=9-2 y=7
Pary to (0;9), (2;7)
x+4y=20
x=0 to 0+4y=20 4y=20 |:4 y=5
x=4 to 4+4y=20 |:4 1+y=5 y=5-1 y=4
Pary to (0;5), (4;4)
