What does the formula 'a = 2*pi*r/dr' mean?

[muratgungor]

I want to ask a question: For a sphere, a = 2*pi*r/dr (where r = radius and dr = thickness). What does this formula mean? Thanks for your help!

 

[TchrWill]

Re: very important

For a sphere, a = 2*pi*r/dr (r=radius dr=thickness). What does this formula mean? Thanks for help!

2*Pi*r is the circumference of a planar circle.

Dividing by a thickness, dr, has no meaning.

 

[Denis]

if you're after the surface area of a sphere: 4pi(r^2) , or pi(d^2)