I would like to write an expression of certain variables into a different form, by using a set of definitions. This may sound like a silly question, yet I really am troubled on how to get on. I'll give out an example, to clarify. Say I have:
And that I would like to define the following factors:
How can I ask mathematica to write $r$ in this form:
By hand, this is obtained by simply dividing the two sides of the fraction by $v$. How can this be managed with Mathematica?