# Geometric series problem

1. Oct 4, 2011

### Jimmy84

Geometric series problem urgent

1. The problem statement, all variables and given/known data

Calculate the geometric series of Ʃfrom n=1 to infinity of 1/n

2. Relevant equations

3. The attempt at a solution
I dont know how to start solving, how can I solve this? I have test about this tomorrow I really need some help please.

2. Oct 4, 2011

### Staff: Mentor

Re: Geometric series problem urgent

First off, what is a geometric series? Are you sure that your series is a geometric series?

3. Oct 4, 2011

### Jimmy84

Re: Geometric series problem urgent

the formula is Ʃ from n=0 to ∞ of a(r)^n is equal to a/(1-r)

I was told to use the geoemtric series and to solve for that. but I dont know any general process or any way to do that. how can I start to solve that?

4. Oct 4, 2011

### Staff: Mentor

Re: Geometric series problem urgent

The general term of a geometric series looks like this: ark. Does your series look like this?

It would be helpful to see the exact wording of your problem. What you have makes almost no sense.

5. Oct 4, 2011

### Jimmy84

Re: Geometric series problem urgent

thats what I have there arent many details i solved some similar problems for instance

Ʃ from n = 0 to ∞ of 1/2^n by subsituing this in the a/(1-r) expression the result was 2

but on this problem I dont see how could I make such a substitution.

6. Oct 4, 2011

### SammyS

Staff Emeritus
Re: Geometric series problem urgent

Are you sure that the word 'geometric' is in the problem in your book , wherever you got it.

This is a well known series that doesn't converge.

7. Oct 4, 2011

### Jimmy84

Re: Geometric series problem urgent

Yes it is there

8. Oct 4, 2011

Re: Geometric series problem urgent

Ʃfrom n=1 to infinity of 1/n..this is harmonic series where the n is to the power of 1..
i just learned this in my class

9. Oct 5, 2011

### SammyS

Staff Emeritus
Re: Geometric series problem urgent

Writing out the first bunch of terms gives:

1 + 1/2

+ 1/3 + 1/4     This is greater than 1/2, because 1/3 > 1/4

+ 1/5 + 1/6 + 1/7 + 1/8    > 1/2, because each fraction is at least 1/8

+ 9 + 1/10 + 1/11 + 1/12 + 1/13 + 1/14 + 1/15 + 1/16  > 1/2, because each fraction is at least 1/16

+ ...

If you go far enough, you can exceed any number you like.

10. Oct 5, 2011

### Staff: Mentor

Re: Geometric series problem urgent

Moderator's note: Thread moved to Calculus & Beyond section.

11. Oct 5, 2011

### flyingpig

Re: Geometric series problem urgent