# Math Help - Series and sequences

1. ## Series and sequences

Can somebody teach me how to solve this question? Please…

Sorry... since i don't know how to write the symbols here... so i used attachment...

2. ## Re: Series and sequences

Originally Posted by AuXian
Show that $\sum_{n=1}^r\frac{r^2+r^{-1}}{r^2+r}=\frac{n^2}{n+1}$
So, are you summing r constants (i.e., expressions that don't depend on n)?

3. ## Re: Series and sequences

If it's $\sum_{r = 1}^n \frac{r^2 + r^{-1}}{r^2 + r} = \frac{n^2}{n+1}$, then it isn't even true.

$n =1:$ LHS $= \frac{1^2 +1^{-1}}{1^2 + 1} = \frac{2}{2} = 1$. RHS $= \frac{1^2}{1+1} = \frac{1}{2}$.

$n =2$: LHS $= (1) + \frac{2^2 +2^{-1}}{2^2 + 2} = 1 + \frac{4.5}{6} = \frac{7}{4}$. RHS $= \frac{2^2}{2+1} = \frac{4}{3}$.

4. ## Re: Series and sequences

Originally Posted by emakarov
So, are you summing r constants (i.e., expressions that don't depend on n)?
ya... only the final step will convert r to n... It is needed to show that LHS=RHS, the LHS will be used. My problem is, I don't know how to simplify the earlier part (about r)...

5. ## Re: Series and sequences

Originally Posted by AuXian
only the final step will convert r to n...
I am not sure what this means. Please write the question correctly.

6. ## Re: Series and sequences

Originally Posted by emakarov
I am not sure what this means. Please write the question correctly.
What i wrote there is a complete question....

7. ## Re: Series and sequences

Originally Posted by AuXian
What i wrote there is a complete question....
And yet you had to add the phrase "only the final step will convert r to n," the meaning of which I don't understand. Even worse, the left-hand side of the equation in the quote in post #2 does not depend on n (n is a bound variable used as the summation index) while the right hand side does. And if n and r are reversed, then, as post #3 shows, the equation is incorrect.