December 17th, 2017, 07:42 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 12:08 PM. 
February 20th, 2018, 10:20 PM  #2 
Global Moderator Joined: Dec 2006 Posts: 18,719 Thanks: 1536 
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 12:58 PM. 

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