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Calculati X² + 1/X². Stiind ca X + 1/x=9.X∈R*

Răspuns :

x+1/x=9 Ridicam la patrat => x^2 +2×x×1/x+1/x^2=81 => x^2 +1/x^2+2=81 => x^2+1/x^2=79