- #1
BraedenP
- 96
- 0
Homework Statement
I feel bad asking another question after I just asked one yesterday, but I'm really close this time, I think!
I have:
[tex]\sum_{n=2}^{\infty}\frac{n^2-n}{2^n}[/tex]
And need to find the sum.
Homework Equations
[tex]\sum_{n=1}^{\infty}nx^{n-1}=\frac{1}{(1-x)^2}[/tex]
The Attempt at a Solution
I have refectored this sum into the form:
[tex]\sum_{n=1}^{\infty}\frac{n^2+n}{2^{n+1}}[/tex]
and can then split it into its two terms.
When finding the sum of the term [itex]\frac{n}{2^{n+1}}[/itex] by factoring out 1/4 and using the formula above, I get 1/4, however, when the sum should be 1. Am I not applying this formula properly?
Additionally, how can I apply the above formula to the term [itex]\frac{n^2}{2^{n+1}}[/itex]? I can again factor out 1/4, but then I'm left with an n2 rather than n.
Guidance for any of these steps would be awesome!