TS EAMCET 9-Sep-2020 Shift 2 Solved Paper

Let r be the radius, h be the slant height and l be the slant height of a cone of semi vertical angle 45∘, then, r=h and l=√2h
Let h=20 and h+∆h=20.025⇒∆h=0.025
Let S be surface area, then
Also, at h=20
We have, S=400√2π