- #1
Battlemage!
- 294
- 45
Homework Statement
Find the interval of convergence of the infinite series:
∞
∑ (x-1)n / 2n
n = 1
Homework Equations
Using the ration test. It converges if the absolute value of the limit of f(n+1)/f(n) as n -> ∞ < 1.
Well, I hope that's how you write it. I'm sure you guys know how to use the ration test.
The Attempt at a Solution
I actually believe I have the answer. But I have no way of knowing if it is right.
Here is my answer:
The interval of convergence is -1 < x < 3.
I got this by using the ratio test, and then eliminating factors of (x-1)n and 2n (after expanding the exponents), leaving me with the limit of
lim (x-1)/2 as n -> ∞
Then, since there is no n, then that limit IS (x -1)/2 (unless I'm totally off)
And the absolute value of that has to be less than 1 for it to converge, so
-1 < (x-1)/2 < 1
-2 < x - 1 < 2
-1 < x < 3
Is this correct? Do you need me to post the part where I canceled out terms before I took the limit?
Thanks!