document.write( "Question 233136: A cylindrical can is to have volume 300 cubic centimetres. Find its height and its
\n" ); document.write( "radius if the total surface area (and hence the total amount of material used) is minimum.
\n" ); document.write( "[The volume is given by V = r2h, and the surface area is S = 2rh + 2r2, where r is the
\n" ); document.write( "radius and h is the height.
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Algebra.Com's Answer #172178 by ankor@dixie-net.com(22740)\"\" \"About 
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A cylindrical can is to have volume 300 cubic centimetres. Find its height and its
\n" ); document.write( "radius if the total surface area (and hence the total amount of material used) is minimum.
\n" ); document.write( "[The volume is given by V = r2h, and the surface area is S = 2rh + 2r2, where r is the radius and h is the height.
\n" ); document.write( ":
\n" ); document.write( "Find h in terms of the Volume
\n" ); document.write( "\"pi%2Ar%5E2%2Ah\" = 300
\n" ); document.write( "h = \"300%2F%28pi%2Ar%5E2%29\"
\n" ); document.write( ":
\n" ); document.write( "Surface area
\n" ); document.write( "S = \"2%2Api%2Ar%2Ah\" + \"2%2Api%2Ar%5E2\"
\n" ); document.write( "Replace h with \"300%2F%28pi%2Ar%5E2%29\"
\n" ); document.write( "S = \"2%2Api%2Ar%2A%28300%2F%28pi%2Ar%5E2%29%29\" + \"2%2Api%2Ar%5E2\"
\n" ); document.write( "we can cancel pi*r
\n" ); document.write( "S = \"2%28300%2Fr%29\" + \"2%2Api%2Ar%5E2\"
\n" ); document.write( "S = \"%28600%2Fr%29\" + \"2%2Api%2Ar%5E2\"
\n" ); document.write( ":
\n" ); document.write( "Plot the equation \"2%2Api%2Ax%5E2%2B%28600%2Fx%29\":
\n" ); document.write( "\"+graph%28+300%2C+200%2C+-4%2C+8%2C+-100%2C+400%2C+2%2Api%2Ax%5E2%2B%28600%2Fx%29%29+\"
\n" ); document.write( "With the help of a TI83, minimum on this graph: x=3.628, (Min SA ~ 248 sq/cm)
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\n" ); document.write( "hence r = 3.628 cm is the radius
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\n" ); document.write( "Find the height
\n" ); document.write( "h = \"300%2F%28pi%2A3.628%5E2%29\" = 7.255 cm is the height
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\n" ); document.write( "Check this by finding the volume with this r and h
\n" ); document.write( "V =\"pi%2A3.628%5E2%2A7.255\"
\n" ); document.write( "V = 300.00
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