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Calculati x²+[tex] \frac{1}{ x^{2} } [/tex] ,stiind ca x-[tex] \frac{1}{ x } [/tex]=4 (x[tex] \neq 0[/tex]

Răspuns :

( x + 1/x)²= 4² →

x² + 2x/x + 1²/x² = 16 →

x² + 2 + 1/x²= 16 →

x² + 1/x² = 14.

[tex]\it x-\dfrac{1}{x} =4\Leftrightarrow \left(x-\dfrac{1}{x}\right)^2 =4^2\Leftrightarrow x^2-2\cdot x\cdot\dfrac{1}{x} +\dfrac{1}{x^2} =16 \Leftrightarrow \\\;\\ \\\;\\ \Leftrightarrow x^2+\dfrac{1}{x^2} -2 =16 \Leftrightarrow x^2+\dfrac{1}{x^2} =16 +2 \Leftrightarrow x^2+\dfrac{1}{x^2} =18. [/tex]