Let P= (V^2)R / (R+r)^2

Question

Calculate dP/dr, assuming that r is variable and R is constant.

Answer 1

P= (V^2)R / (R+r)^2
Assuming V,R are constants and use chain rule
dP/dr
= dP/d(R+r) * d(R+r)/dr
= d[(V^2)R/(R+r)^2]/r
=-2V^2R/(R+r)3
=-2V^2R/(R+r)3

Answer 2

-2V^2R/(R+r)3

Answer 3

(-2V^2R)/(R+r)^3