daca x+y+z=6 si xy+yz+zx=13, atunci
{x}^{2} + {y +}^{2} + {z}^{2} = ?
PS : E URGENT !!! DAU COROANA


Răspuns :

(x+y+z)^2=x^2+y^2+z^2+2(xy+xz+yz)
x^2+y^2+z^2=(x+y+z)^2 -2(xy+xz+yz)
x^2+y^2+z^2 =6^2 -2(13)=36-26=10