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Cel mai inteligent răspuns!
2014-06-05T18:12:40+03:00
 foloseste formula (a+b+c)²=a²+b²+c²+2(ab+bc+ac)

(x+y+z)²=x²+y²+z²+2(xy+yz+xz)=216+2*230=676
x+y+z=26

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