Question 1070502
P = E^2R/(R+r)^2, with r = const
We need to maximize this expression with respect to R, so we need to solve dP/dR = 0
If you perform the differentiation, you should be left with dP/dR = V^2/(R+r)^2 -2V^2R/(R+r)^3 = 0
Multiply both sides by (R+r)^2/V^2:
1 - 2R/(R+r) = 0 -> R + r = 2R -> R = r