Răspuns:
1. a) din x+y=2 scoatem x= 2-y si inlocuim in a 2 ecuatie
3*(2-y)+2y=3 6-3y+2y=3 6-3=y y=3
x= 2-3=-1 x=-1
b) -x+y=4 scoatem x=y-4 inlocuim in a 2 ecuatie
5y-20+2y=8 7y=28 y=4
x=4-4=0 x=0 (pe urmatoarele le faci dupa model)
2. a) [tex]\left \{ {{x+y=5} \atop {x-y=1}} \right.[/tex] se aduna ecuatiile
x+y+x-y=5+1 2x=6 => x=3
y=x-1= 3-1=2 y=2
b) [tex]\left \{ {{x+y=4} \atop {2x-y=-1}} \right.[/tex] se aduna ecuatiile
x+y+2x-y=4-1 3x=3 => x=1
y=4-x=4-1=3 y=3 (dupa model le faci)
3. a) [tex]\left \{ {{x+2y=-1} \atop {4x-2y=6}} \right.[/tex] se aduna ecuatiile
x+2y+4x-2y= 6-1 5x=5 => x=1
2y=-1-x =-1-1=-2 y=-2: 2= -1 y=-1
b) [tex]\left \{ {{3x+4y=6} \atop {x-4y=-14}} \right.[/tex] se aduna ecuatiile
3x+4y+x-4y= 6-14 4x= -8 x= -8:4= -2 x=-2
4y=6-3x= 6+6=12 y=12:4 =3 y=3
