My Math Forum help with limits of sequences

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 December 17th, 2017, 08:42 AM #1 Newbie   Joined: Dec 2017 From: usa Posts: 2 Thanks: 0 help with limits of sequences Hello I really troubled with the following questions $\displaystyle u_n = \left(\frac{2n^3 - 4n^2 + 5}{10n^3 + 100}\right)\cdot2^{-n}$ $\displaystyle w_n = \left(\frac{3n + 2}{4n^2 + 8n + 5}\right)\cdot\left(\frac{(1 - n)^3}{(14 - 5n)^2}\right)$ $\displaystyle e_n = \frac{2^n + 3^{n - 1} + 5^{2n + 2}}{4^{n - 7} + 5^{2n}}$ $\displaystyle b_n = \frac{\left(\frac23\right)^n}{\left(\frac12\right) ^n + \left(\frac{9}{10}\right)^n}$ $\displaystyle S_n = 4\sqrt{n + 3} - \sqrt{n - 1} - 5\sqrt{n + 7} + 2\sqrt{n- 3}$ http://www.interload.co.il/upload/8256588.png I need to calculate the limit of each sequence My main concern is the last 3. Last edited by skipjack; March 21st, 2018 at 01:08 PM.
 February 20th, 2018, 11:20 PM #2 Global Moderator   Joined: Dec 2006 Posts: 20,288 Thanks: 1968 The first expression has a limit of zero, but would have a limit of 1/5 if the $2^{-n}$ weren't present. For the second limit, work out the terms in $n^4$, then divide the numerator and denominator by $n^4$. For the third limit, divide the numerator and denominator by $5^{2n}$. Last edited by skipjack; March 21st, 2018 at 01:58 PM.

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