Răspuns:
Explicație pas cu pas:
a) x + y = 5
4(x+y) = 4 × 5 = 20
______________
b) 2 x + 2 y = 8 [ : 2
x + y = 4
3 x + 3 y = 3 × ( x + y ) = 3 × 4 = 12
___________________________
c)
x - 2 y = 5
y + 3 z = 7 [ × 2
_____________
x - 2 y = 5
2 y + 6 z = 14
______________ adun relatiile
x + 6 z = 5 + 14
x + 6 z = 19