Rezolvati prin metoda substitutiei urmatoarele sisteme:
3x-y=-4
x-3y=-4

4x=9y=21
12x=15y=51
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8x-y=-15
-x+8y=-6

10x+27y=10
-25x+12y=-25

1-4x=y
2-y=x+y

2x-3y=4
-8x+12y=8