a)
y+x/2=13
y-x/2=4
2y=17
y=8,5
x/2+8,5=13
x/2=4.5
x=9
————————————————
b)
x/2+y/3=1/6
x/6-y/4=1/2 | ×(-3)
-x/2+3y/4=-3/2
y/3+3y/4=1/6-9/6
4y/12+9y/12=-8/6
13y/12=-4/3
y=-48/39
y=-16/13
x/2-16/39=6.5/39
x/2=22.5/39
x=45/39
x=15/13
c)
-x+y/3=1/3
x/2-y=-25/18 | ×2
x-2y=-25/9
-5y/3 = -22/9
5y=22/3
y=22/15
22/45-x=1/3
22/45-x=15/45
x=7/45
d)
3(x+y-1)=2x-y+6.5
-2x+9y=-24
3x+3y-3=2x-y+6.5
x+4y=9.5 | ×2
2x+8y=19
17y=-5
y=-5/17
-2x-45/17=-24
2x+45/17=24
2x+45/17=408/24
2x=363/24
x=363/48
