So, how do I solve this to find the value of n ?

Un = (-1)^n (n / n + 4) and I know that Un = 7 / 9 ?

So do you times (-1)^n and ( n / n + 4) ??

Someone help me out here, with explanation please!

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- Sep 27th 2008, 09:43 AMMathematixSequences and series..
So, how do I solve this to find the value of n ?

Un = (-1)^n (n / n + 4) and I know that Un = 7 / 9 ?

So do you times (-1)^n and ( n / n + 4) ??

Someone help me out here, with explanation please! - Sep 27th 2008, 09:55 AMbkarpuz
- Sep 27th 2008, 11:34 AMMathematix
^ From that, I need to know how to find the value of n.

- Sep 27th 2008, 12:55 PMbkarpuz
Are you asking for which $\displaystyle n$ value $\displaystyle u_{n}=\frac{7}{9}$ holds?

If so, $\displaystyle n=14$.

To find the solution, first consider $\displaystyle n=2k$ then $\displaystyle n=2k-1$ for $\displaystyle k\in\mathbb{N}$.

In the first case, you will find $\displaystyle k=7$ ($\displaystyle n=14$) and in the second one $\displaystyle k=-\frac{3}{8}\not\in\mathbb{N}$. - Sep 27th 2008, 01:05 PMJhevon
you are somewhat vague, Mathematix, but if bkarpuz's last post accurately said what you want, then you must solve $\displaystyle \frac n{n + 4} = \frac 79$ for $\displaystyle n$. and note that $\displaystyle n$ must be even. so if you get an odd number, you are wrong