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Demonstrati ca [tex] x^{3} - \frac{1}{ x^{3} } \geq 3(x- \frac{1}{x} )[/tex] oricare ar fi x∈ R, x≥1.

Răspuns :

[tex](x- \frac{1}{x} )^{3}= x^{3}-3x^{2} \frac{1}{x} +3x \frac{1}{x^{2}} - \frac{1}{x^{3}} = x^{3} -3x+3 \frac{1}{x}- \frac{1}{x^{3}} [/tex]
Cum x≥1⇒[tex]x- \frac{1}{x} [/tex]≥0 si rezulta ipoteza
Am rezolvat problema in fisierul atasat.

Vezi imaginea Tstefan