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**Solo** Hey folks.

I still havent got my head round the idea of a series expansion and am stuck on the questions in my homework regard series expansion.

1) What is the series expansion of $\displaystyle ln(1+x^2 / 100)$ and it's radius of conversion?

There is a an x-formula in my textbook which reads $\displaystyle ln x = (x-1) - \frac{1}{2}(x-1)^2 + \frac{1}{3}(x-1)^3 - ...$. First of all I don't exactly understand where it has come from (the explanation isn't clear) and secondly, can I just plug in my "x" is into the formula?

I know the Radius of Convergence is when the function doesn't make sense so for the question the ROC is infinity i.e. it always makes sense?