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Naci granicnu vrednost... 04.11.2011. u 18:45 · pre 182 meseci #1
Pozdrav, na koji nacin da izracunam \lim_{n \to \infty} ({\sqrt{n^2+2n}-n})^n ? Ja dodjem do e^{n {n-\sqrt{n^2+2n} \over n+\sqrt{n^2+2n}}}.
Re: Naci granicnu vrednost... 04.11.2011. u 19:14 · pre 182 meseci #2
e^{\lim_{n\to \infty } n\frac{n-\sqrt{n^2+ 2n}}{n+\sqrt{n^2+ 2n}}}=e^{\lim_{n\to \infty } n\frac{n-\sqrt{n^2+ 2n}}{n+\sqrt{n^2+ 2n}}\frac{n+\sqrt{n^2+ 2n}}{n+\sqrt{n^2+ 2n}}}=e^{\lim_{n\to \infty } n\frac{-2n}{\left(n+\sqrt{n^2+ 2n}\right)^2}}=e^{\lim_{n\to \infty } \frac{-2n^2}{n^2+2n\sqrt{n^2+ 2n}+n^2+2n}}=

=e^{\lim_{n\to \infty } \frac{-2n^2}{n^2\left(1+\frac{2}{n}\sqrt{n^2+ 2n}+1+\frac{2}{n}\right)}}=e^{\lim_{n\to \infty } \frac{-2}{\left(1+2\sqrt{1+ \frac{2}{n}}+1+\frac{2}{n}\right)}}=e^{\frac{-2}{4}}=e^{-1/2}=\frac{1}{\sqrt{e}}

Edit: Ako se ne vidi evo ovako:

n\frac{n-\sqrt{n^2+ 2n}}{n+\sqrt{n^2+ 2n}}=n\frac{n-\sqrt{n^2+ 2n}}{n+\sqrt{n^2+ 2n}}\frac{n+\sqrt{n^2+ 2n}}{n+\sqrt{n^2+ 2n}}=n\frac{-2n}{\left(n+\sqrt{n^2+ 2n}\right)^2}=\frac{-2n^2}{n^2+2n\sqrt{n^2+ 2n}+n^2+2n}=\frac{-2n^2}{n^2\left(1+\frac{2}{n}\sqrt{n^2+ 2n}+1+\frac{2}{n}\right)}=\frac{-2}{\left(1+2\sqrt{1+ \frac{2}{n}}+1+\frac{2}{n}\right)}
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