I am trying to understand this technical note, specifically problem 1 on page 4.
I am quite happy with everything up to equation 2 on page 5. I don't understand where the figure .39D 2/3 has come from nor 48D 2/3 in equation 3.
Can anybody else see where these figures have come from? I've been looking at this for sometime. I realise it is quite a long question but I would be grateful for any help.