Surface area formula proof - integrate circumference of volume of revolution

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SUMMARY

The discussion centers on proving the surface area formula for a cone, specifically πrl, through integration of the circumference of a volume of revolution. The user attempts to derive the formula using the integral ∫2πydx, substituting y with r/hx, and integrating to find πrh. However, the user identifies a discrepancy, as the result does not yield the expected formula πrl. This indicates a misunderstanding in the integration process or the application of limits.

PREREQUISITES
  • Understanding of calculus, specifically integration techniques.
  • Familiarity with the concept of volumes of revolution.
  • Knowledge of the geometric properties of cones.
  • Experience with limits in calculus.
NEXT STEPS
  • Review the derivation of the surface area formula for cones in calculus textbooks.
  • Study the method of volumes of revolution and its applications in geometry.
  • Learn about the use of limits in integration to clarify the approach taken.
  • Explore alternative proofs of the surface area of a cone using different mathematical techniques.
USEFUL FOR

Students studying calculus, particularly those focusing on geometric applications, as well as educators seeking to clarify the proof of surface area formulas in their curriculum.

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Homework Statement


I believe this is intended to be a proof of the formula πrl, surface area of a cone.


Homework 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


The Attempt at a Solution


When I tried this, I got:
∫2πydx
=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!
 
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