Question

What is the interval of convergence of `sum x^(2n) / (2n)!`?

Answer 1

`(-oo, oo)`

Explanation:

This is the series expansion for

`cosh x =` arithmetic mean of `e^x and e^(-x)`

So, the interval of oinvergence `x in (-oo, oo)` is the interval of

convergence for this series.