If "n= 0", then n/(1+b)= 0, not 1, so "n/(1+ b)= 1 is wrong. Going back to your original equation, if n= 0, B= A and b can be any number from 0 to 1.2. Moreover, when n/(1+b) = 1 then b = n - 1
Now if n = 0 then b = -1 (But how this is possible, as b has a minimum value of 0).
You say that b cannot be less than 0 so I guess 0 is a "boundary value" for b but I don't know what other boundary values you are talking about.3. Please check this equation for all boundary values for n and b, and me know if this function is mathematically fine or should I change this.