I've seen this thread:(adsbygoogle = window.adsbygoogle || []).push({});

https://www.physicsforums.com/showthread.php?t=297842

and that is the exact question I need to to answer.

What is the radius of convergence of 1/(1+x^2) expanded about x_0=1?

The problem is, I can only use an argument in real analysis.

I see the answer is sqrt(2), but I cannot get that answer.

I've tried a lot of little manipulations to get different geometric series but I can't seem to get it.

Thanks

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# Radius of convergence: 1/(1+x^2) about 1, using only real analysis

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