document.write( "Question 1104057: the total area of a cylinder is 40pi. If h=8, find r. \n" ); document.write( "

Algebra.Com's Answer #718780 by greenestamps(13200) $\"\"$ $\"About$

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\n" ); document.write( "Given that the height is 8, the total surface area is $\"2%28pi%29r%5E2%2B2%28pi%29rh+=+2%28pi%29r%5E2%2B16%28pi%29r\"$

\n" ); document.write( "Given that the total surface area is 40pi,

\n" ); document.write( " $\"2%28pi%29r%5E2%2B16%28pi%29r+=+40pi\"$
\n" ); document.write( " $\"2%28pi%29r%5E2%2B16%28pi%29r-40%28pi%29+=+0\"$
\n" ); document.write( " $\"r%5E2%2B8r-20+=+0\"$ [dividing out the common factor 2pi]
\n" ); document.write( " $\"%28r%2B10%29%28r-2%29+=+0\"$

\n" ); document.write( "r = -10 or r=2; since this is the radius of the cylinder, we reject the negative solution.

\n" ); document.write( "The radius of the cylinder is 2. \n" ); document.write( "

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