- #1
Schniz2
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Homework Statement
Find the centre and radius of convergence:
[tex]\stackrel{\infty}{n=1}\sum n.(z+i\sqrt{2})^{n}[/tex]
Homework Equations
1) Ratio test [tex]\left|\frac{a_{n+1}}{a_{n}}\right|<1[/tex]
2) Textbook uses [tex]\stackrel{lim}{n-> \infty}\left|\frac{a_{n}}{a_{n+1}}\right|[/tex]
The Attempt at a Solution
using 1) and taking the limit as n -> infinity i end up with
[tex]\left|z+i\sqrt{2}\right|<1[/tex]
...but then don't know where to go
using 2) i end up with
[tex]\left|\frac{1}{z+i\sqrt{2}}\right|[/tex]
...
:S
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