# Homework Help: Problem while playing with Bessel functions

1. Nov 30, 2015

### saybrook1

1. The problem statement, all variables and given/known data
I have run in to a number of problems while working through problems regarding Bessel and Modified Bessel Functions. At one point I run in to $i^{m}e^{\frac{im\pi}{2}}$ and it needs to equal $(-1)^m$ but I'm not sure how it does. This came up while trying to solve an identity for a modified Bessel function in problem 14.5.2 in Arfken and Weber 'Mathematical Methods for Physicists'. Any help would be greatly appreciated, thank you.

2. Relevant equations
$i^{m}e^{\frac{im\pi}{2}}$=$(-1)^m$ but how??

3. The attempt at a solution
I solved for this by expanding the exponent in to cos and sin but I wind up with $i^{m} [cos\frac{m\pi}{2}+(-1)^{m}\sin\frac{m\pi}{2}]$ and don't know how that can equal $(-1)^m$

2. Nov 30, 2015

### Samy_A

There is an error in $i^{m} [cos\frac{m\pi}{2}+(-1)^{m}\sin\frac{m\pi}{2}]$, that should be $i^{m} [cos\frac{m\pi}{2}+i\sin\frac{m\pi}{2}]$

An easy way to solve your exercise it to consider four case separately: $m=0, m=1,m=2, m=3$.

3. Nov 30, 2015

### saybrook1

You're right, I just typed it out incorrectly. Okay, I'll try and consider those cases; Thank you.

4. Nov 30, 2015

### SteamKing

Staff Emeritus
If you express i in polar form, you have i = e(iπ/2). From there, you should be able to find im in polar form quite easily and then to find the product of im and e(imπ/2) in polar form.

Soon after that, a vist from your Uncle Bob can be expected.