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
Cum x≥1⇒[tex]x- \frac{1}{x} [/tex]≥0 si rezulta ipoteza