Răspuns :
X1^2+x2^2+x3^2=S1^2+2S2
S1: x1+x2+x3= -b/a = -2
S2: x1x2+x1x3+x2x3= c/a= -5
Atunci X1^2+x2^2+x3^2=S1^2+2S2
(-2)^2 -2•(-5)=4 +10 =14
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