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dacă x+3y=7 ; x-y+ 2z=5 ; x+y+z=?

Răspuns :

Aduni primele 2 ecuatii: x + 3*y + (x - y + 2*z) = 7 + 5 => 2*x + 2*y + 2*z = 12 , scoti 2 in fata 2*(x + y + z) = 12 => x + y + z = 6
X+3Y=7
X-Y+2Z=5
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2X+2Y+2Z=12
2(X+Y+Z)=12
X+Y+Z=12÷2
X+Y+Z=6