# Infinite series n/2^n-1

1. Feb 10, 2009

### djuiceholder

1. The problem statement, all variables and given/known data
so I have learned how to do different problems of series.
but theres this problem that I spent hours last night but could not come up with anything.
which is-

n/2^(n-1)
n=1

2. Relevant equations

I have no idea

3. The attempt at a solution
so from there i was able to take out 2 and end up with: 2 n /(2^n)

i dont know how to do after that. however, i thought about doing (1/2)^n but then again it does not make sense to me.

help needed. i will appreciate that. thanks
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Feb 10, 2009

### Staff: Mentor

Why have you cross-posted this problem to this forum and the Precalc forum?

3. Feb 10, 2009

### Enjoicube

Something tells me that the ratio test could helo here.

4. Feb 10, 2009

### Dick

If you want to show the series converges, the ratio test can help. If you want to find the sum, the ratio test can't help. Hint: this looks like it's related to the series 1+x+x^2+x^3+.... Take a derivative. Now figure out what to put x equal to.

5. Feb 12, 2009

### djuiceholder

i was supposed to evaluate it. I dont know how though

6. Feb 12, 2009

### djuiceholder

i posted this problem on a different folder and i was warned because it was a wrong place to post. anyways, i think i took it off