Find the rate of change of the total surface area of a cylinder of radius  and height , when the radius varies.

Explanation

Let `T` be the total surface area of a cylinder. Then,



`{T}=2 pi r(r+h)`



Since the radius varies, we differentiate the total surface area w.r.t. radius `r`.


Now,



`frac{d T}{d r}=frac{d}{d r}[2 pi r(r+h)] `


...