# Thread: Series formula

1. ## Series formula

Any help with this question would be very much appreciated

2. ## Re: Series formula

Rationalize the denominator, and you will find you have a telescoping series.

3. ## Re: Series formula

Multiply nominator and denominator by the conjugate expression ( same expression with - sign in the middle) of the denominator....
the rest is easy as Mark Fl said in his post

4. ## Re: Series formula

I have rationalized the denominator but I don't actually know where to go from there, that is why I am posting this, I don't know the process

5. ## Re: Series formula

What did you get when you rationalized the denominator?

If you show your work, then we can better see where you are and how best to help.

6. ## Re: Series formula

sqrt(r+1)-sqrt(r)

7. ## Re: Series formula

Correct, so we now have:

$\sum_{r=1}^n\left(\sqrt{r+1}-\sqrt{r} \right)=\sum_{r=1}^n\sqrt{r+1}-\sum_{r=1}^n\sqrt{r}$

Now, can you change the index of summation on one of the sums so that you have the same summand in each?