- #1

- 51

- 5

## Homework Statement

## Homework Equations

## The Attempt at a Solution

Working with equation 18.1 i found that

However, this obviously is not the equation in 18.3.

I found a source talking about this problem, and they get a similar equation

http://file.scirp.org/pdf/JAMP_2014031310562629.pdf

I have no clue where to go with this problem. Where is the 2 d theata / dl term coming from?