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[tex] x^{2} +3x-5=0[/tex] , sa se calculeze [tex] x1^{2} + x2^{2} = ?[/tex]

Răspuns :

[tex]x_1^2+x_2^2=S^2-2P, \text{ unde }\\ S=x_1+x_2=-\frac{b}{a}=-3\\ P=x_1x_2=\frac{c}{a}=-5\\ \text{ Asadar, } \\x_1^2+x_2^2=9+10=19 [/tex]
x1^2+x2^2=(x1+x2)^2-2x1*x2
dupa Viette x1+x2=-3 si x1x2=-5
deci  x1^2+x2^2=9+10=19