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a)3x+3y daca x+y=15
b)x(y+z) daca xy+XZ=10
c) x daca xy+xz=-12 si y+z=-3


Răspuns :

x+y=15
3x+3y=3(x+y)=3×15=45

xy+xz=10
x(y+z)=xy+xz=10

xy+xz=-12
y+z=-3
xy+xz=x(y+z)
x•(-3)=-12
x=4
.
Dai factor comun pe 3:
a) 3•(x+y)=3•15=45
b) Inmulteste fiecare termen cu x
x•y+x•z=10
c) Iara factor comun x•(y+z)=-12
x•-3=-12
x= 4