Question 123318
The given expression is:


{{{V = 2R/(R - r)}}} 


By cross - multiplying, we get:


{{{(R - r) = 2R/V}}} 


Adding r - 2R/V on both sides, we get: 


{{{(R - 2R/V)}}} = r 


OR 


{{{(RV - 2R)/V = r}}} 



Thus the solution in which "r" is the subject.