Optimization find radius problem

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Discussion Overview

The discussion revolves around an optimization problem involving the surface area of a solid formed by two hemispheres attached to a right circular cylinder, with a fixed total volume of 12 cubic centimeters. Participants are seeking to determine the radius of the cylinder that minimizes the surface area.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant requests assistance with the optimization problem, expressing urgency due to time constraints.
  • Another participant asks for clarification on what the original poster has attempted so far in solving the problem.
  • A participant outlines a step-by-step approach to solve the problem, including writing formulas for volume and surface area, substituting variables, and finding the radius that minimizes surface area.
  • A later reply provides specific formulas for surface area and volume, derives the expression for height in terms of radius, and calculates the derivative of the surface area to find critical points.
  • The same reply suggests testing points around the calculated radius to confirm it is a minimum.

Areas of Agreement / Disagreement

There is no explicit consensus on the solution, as participants are still discussing the problem and exploring different approaches. The original poster has not confirmed any findings.

Contextual Notes

The discussion includes assumptions about the formulas used for volume and surface area, as well as the method for finding the minimum. There may be unresolved steps in the mathematical reasoning presented.

Who May Find This Useful

Students or individuals interested in optimization problems in calculus, particularly those involving geometric solids.

calvinnn
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optimization problem!

OKOK running out of time! CAn anyone please help me with this problem:

Surface Area A solid os formed by adjoining two hemispheres to the ends of a right circular cylinder. The total volume of the solid is 12 cubic centimeters. Find the radiusof the cylinder that produces the minimum surface area.

if anyone can help me with this, ill be VERY grateful!
 
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Exactly what have you tried so far?
 
1. Call the length of the cylinder l and the radius r. Write down the formula for the volume of the figure (its a cylinder and a sphere) and set that equal to 12. Solve for l.

2. Write down the formula for surface area (again, lateral area of a cylinder, area of a sphere) and replace l by the formula from 1 so that you have a function of r only.

3. Find the value of r that minimizes that function.
 
Q: Surface Area A solid os formed by adjoining two hemispheres to the ends of a right circular cylinder. The total volume of the solid is 12 cubic centimeters. Find the radiusof the cylinder that produces the minimum surface area.

A:

SA=2 π r2 + 2 π r h

V=πr^2h, V=12

h=12/(πr^2)

thus, SA=(2πr^2)+(2πr)(12/(πr^2))

SA'=4πr-(24/r^2) To find the minimum, set SA' to zero.

0=4πr-(24/r^2) r=6^(1/3)/π^(1/3), approx. 1.2

Test a point on either side of r=1.2 to make sure that it is a minimum.
 
Last edited:

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