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# Tag Archives: Series

## Series of Bessel function

Let denote the Bessel function of the first kind. Prove that

Solution

The Jacobi – Anger expansion tells us that

(1)

Hence by Parseval’s Theorem it follows that

## Zeta logarithmic series

Let denote the zeta function. Prove that

Solution

## Arctan series

Evaluate the series

Solution

One can argue that the same technique used to evaluate the sum here can be used here as well. Unfortunately, this is not the case as the sum does not telescope. However the technique used here is the way to go.

First of all we note that

However, it is known that

(1)

Let . We note that . Hence,

which is now a matter of calculations. The sum is equal to

## A telescoping arctan series

Evaluate the sum

Solution

First of all note that:

Hence letting we have that

## An arctan series

Prove that

Solution

The key ingredient is the observation . Then we note that

Using the arg’s property we get that

Hence the initial sum telescopes;

since which explains why pops up.

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