a) x+y=15
x-y=3
_____________
x=18
y=15-18
y=-3
b) x+y=9/ · -1
-x-y=-9
x+3y=2
______________
2y=-8
y=-4
x=9-4
x=5
c) 3x-3y=7/· -1
-3x+3y=-7
4x-3y=3
_______________
x=-4
4x-3y=3
4·(-4)-3y=3
-16-3y=3
-3y=19
y=19/3
restul nu inteleg dar cred ca ai inteles ideea :)
