1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Surface area formula proof - integrate circumference of volume of revolution

  1. Nov 19, 2011 #1
    1. The problem statement, all variables and given/known data
    I believe this is intended to be a proof of the formula πrl, surface area of a cone.

    2. Relevant equations
    A complete volume of revolution gives you a cone - the height h is the x value on a graph, the radius r is the y value. The y intercept is zero, therefore y=r/hx . All integration is with lim h→0

    3. The attempt at a solution
    When I tried this, I got:
    =2π∫r/hx dx
    =2πr/h∫x dx
    =2πr/h ∫x2/2
    =πrh! So why has this not worked? I need this to give πrl!
  2. jcsd
  3. Nov 20, 2011 #2
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook