1. ## Arithmetic progression

Given the sum of the first n terms of a series is given by Sn =n²+2n for n ＞1. how to determine an expression for the rth term , Ur? I have totally no idea for this question...can anyone help me?

Algebra

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2. ## Re: Arithmetic progression

$S_n=U_1+U_2+\ldots +U_{n-1}+U_n$

$S_{n-1}=U_1+U_2+\ldots +U_{n-1}$

$U_n=S_n-S_{n-1}$

3. ## Re: Arithmetic progression

If you're not too busy or tired, use google.

4. ## Re: Arithmetic progression

Originally Posted by DenisB
If you're not too busy or tired, use google.
But if people did that, there would never be any easy questions that I could answer!

5. ## Re: Arithmetic progression

Originally Posted by goldsomecriss
I have totally no idea for this question
Funny Halls!
Doesn't it make you wonder why students are given
problems that they have NO IDEA how to solve?!

6. ## Re: Arithmetic progression

No, I do that to my students all the time! Of course, I'm mean!