4.
a)
x+2y=4 | *2
-2x+y=-3
2x+4y=8
-2x+y=-3
5y=5
y=5/5
y=1
-2x+1=-3
x=2
b)
-2x+y=1 |*(-2)
3x+2y=-5
4x-2y=-2
3x+2y=-5
7x=-7
x=-7/7
x=-1
-2*(-1)+y=1
2+y=1
y=1-2
y=-1
c)
-x+2y=1 |*(-3)
-3x+6y=2
3x-6y=-3
-3x+6y=2
0=-1
deci (x,y) apartine multimii vide.
d)
2x+y=1
-2x-y=-1 din ce avem aici totul este egal cu 0
0=0
x apartine multimii R
5.
a)
x/2-y/3=2 |*6
x/6+y=4 |*6
3x-2y=12
x+6y=24 |*(-3)
3x-2y=12
-3x-18y=-72
-20y=-60
y=-60/-20
y=3
3x-2*3=12
x=6
b)
x/3+y/4=7 |*12
-x/4+y/3=1 |*12
4x+3y=84 |*3
-3x+4y=12 |*4
12x+9y=252
-12x+16y=48
25y=300
y=300/25
y=12
-3x+4*12=12
-3x+48=12
-3x=12-48
-3x=-36
x=-36/-3
x=12
c)
x/2+y/5=1 |*10
x/3-y/5=2 |*15
5x+2y=10
5x-3y=30 |*(-1)
5x+2y=10
-5x+3y=-30
5y=-20
y=-20/5
y=-4
5x+2*(-4)=10
5x-8=10
5x=10+8
5x=18
x=18/5
