Relative Velocity of locus of curves

[bugatti79]

Hi Folks,
I am struggling to see how eqn 4.1.17 is arrived at using using eqn 4.1.10 at bottom of attachment. Its not clear to me what $$\frac{d \phi}{dt}$$ is...apart from what is given in eqn 2.1.30...
Any ideas?
Thanks

 

[phinds]

I have an idea ... post a pic that can be read

 

[bugatti79]

Hi.
Ok..I will try another picture again tomorrow.

I think there should be enough resolution in the photo when you zoom in.
Thanks

 

[bugatti79]

Hi,

This is the best I can do regarding a readable picture where I have pasted the relevant eqns.

Thanks