document.write( "Question 117465: hI1
\n" ); document.write( "please help me with this. I have done so many questions before but this one just doesnt give the right answer?? any help would be apreciated\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "The volume of a library is 20000 m (cubed) We have to minimize the Surface area to ignore the heat loss.Dtermine the dimensions of the building that will best give us teh minimum Surface area.??\r
\n" ); document.write( "\n" ); document.write( "thanks for any help coming this way.
\n" ); document.write( "

Algebra.Com's Answer #85472 by Fombitz(32388)\"\" \"About 
You can put this solution on YOUR website!
For a cylindrical room, h is height, r is the radius.
\n" ); document.write( "\"V+=+%28pi%29r%5E2h\" Volume of the cylinder
\n" ); document.write( "\"S+=+2%28pi%29r%5E2%2B2%28pi%29rh\" Surface area of top and bottom plus unrolled side
\n" ); document.write( "\"V=20000=%28pi%29r%5E2h\"
\n" ); document.write( "You can rearrange the equation to solve for h as a function of r.
\n" ); document.write( "\"h=20000%2F%28%28pi%29r%5E2%29\"\r
\n" ); document.write( "\n" ); document.write( "Then substitute that back into the surface area equation,
\n" ); document.write( "\"S+=+2%28pi%29r%5E2%2B2%28pi%29rh\"
\n" ); document.write( "\"S+=+2%28pi%29r%5E2%2B2%28pi%29r%2820000%2F%28%28pi%29r%5E2%29%29\"
\n" ); document.write( "\"S+=+2%28pi%29r%5E2%2B40000%2Fr\"
\n" ); document.write( "Plot S using various values of r and look for a minimum.
\n" ); document.write( "8.1, 5350.
\n" ); document.write( "9.1, 4915.
\n" ); document.write( "10.1, 4601.
\n" ); document.write( "11.1, 4377.
\n" ); document.write( "12.1, 4225.
\n" ); document.write( "13.1, 4131.
\n" ); document.write( "14.1, 4085.
\n" ); document.write( "15.1, 4080.
\n" ); document.write( "16.1, 4112.
\n" ); document.write( "17.1, 4175.
\n" ); document.write( "18.1, 4267.
\n" ); document.write( "19.1, 4385.
\n" ); document.write( "20.1, 4527.
\n" ); document.write( "Looks like a minimum at r=15.1.
\n" ); document.write( "Now that you have r, go back to your equation for h and solve.
\n" ); document.write( "\"h=20000%2F%28%28pi%29r%5E2%29\"
\n" ); document.write( "\"h=20000%2F%28%28pi%2915.1%5E2%29\"
\n" ); document.write( "\"h=27.9%29\"
\n" ); document.write( "Make sure to check your answer.
\n" ); document.write( "\"V+=+%28pi%29r%5E2h\"
\n" ); document.write( "\"V+=+%28pi%2915.1%5E2%2A27.9\"
\n" ); document.write( "\"V+=+19985\"
\n" ); document.write( "Close enough.
\n" ); document.write( "r=15.1 m, h=27.9 m
\n" ); document.write( "
\n" );