`I = (2V/r)+2r`
`I = (2V+2r^2)/r`
`Ixxr = 2V+2r^2`
`2r^2-Ir+2V = 0`
This is a quadratic equation.Solution for this equation is given by;
`r = (-(-I)+-sqrt((-I)^2-4xx2(2V)))/(2xx2)`
So this will give you two answers for r.
`r = (I+sqrt(I^2-16V))/(4)`
`r = (I-sqrt(I^2-16V))/(4)`
By the look of it this letters denote the symbols of a circuit.
V = voltage
I = current
r = resistance
Usually resistance is a positive component not like voltage or current. So here we have to accept the positive answer for 'r' once you solve it.