document.write( "Question 1029100: Calculus:\r
\n" ); document.write( "\n" ); document.write( "A fence must be built to enclose a rectangular area of 5000 ft^2. Fencing material costs $1 per foot for the two sides facing north and south and ​$2 per foot for the other two sides.
\n" ); document.write( "Find the cost of the least expensive fence.
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Algebra.Com's Answer #644148 by josmiceli(19441)\"\" \"About 
You can put this solution on YOUR website!
You are asked to minimize expense
\n" ); document.write( "Let \"+s+\" = the length of one of the sides
\n" ); document.write( "that face north and south and costs $1 / ft
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\n" ); document.write( "Let \"+A+\" = area enclosed by fences
\n" ); document.write( "\"+A+=+s%2A%28+5000%2Fs+%29+\"
\n" ); document.write( "So, the sides are \"+s+\" and \"+5000%2Fs+\"
\n" ); document.write( "------------------
\n" ); document.write( "Let \"+P+\" = the perimeter of the area fenced in
\n" ); document.write( "The perimeter of the area is:
\n" ); document.write( "\"+P+=+2s+%2B+2%2A%28+5000%2Fs+%29+\"
\n" ); document.write( "-----------------------
\n" ); document.write( "Let \"+C+\" = the cost of fencing in the area
\n" ); document.write( "\"+C+=+1%2A%28+2s+%29+%2B+2%2A2%2A%28+5000%2Fs+%29+\"
\n" ); document.write( "\"+C+=+2s+%2B+20000%2Fs+\"
\n" ); document.write( "\"+C1+=+2+-+20000+%2F+s%5E2+\"
\n" ); document.write( "Set the 1st derivative, \"+C1+=+0+\"
\n" ); document.write( "\"+0+=+2+-+20000+%2F+s%5E2+\"
\n" ); document.write( "\"+20000+%2F+s%5E2+=+2+\"
\n" ); document.write( "\"+s%5E2+=+10000++\"
\n" ); document.write( "\"+s+=+100+\"
\n" ); document.write( "and
\n" ); document.write( "\"+5000%2Fs+=+5000%2F100+\"
\n" ); document.write( "\"+5000%2Fs+=+50+\"
\n" ); document.write( "-----------------------
\n" ); document.write( "Plug these results back into original equation
\n" ); document.write( "\"+C+=+2s+%2B+20000%2Fs+\"
\n" ); document.write( "\"+C+=+2%2A100+%2B+20000%2F100+\"
\n" ); document.write( "\"+C+=+200+%2B+200+\"
\n" ); document.write( "\"+C+=+400+\"
\n" ); document.write( "The least expensive fence costs $400
\n" ); document.write( "---------------------------------
\n" ); document.write( "check answer:
\n" ); document.write( "\"+A+=+s%2A%28+5000%2Fs+%29+\"
\n" ); document.write( "\"+A+=+100%2A50+\"
\n" ); document.write( "\"+A+=+5000+\"
\n" ); document.write( "OK -here's the plot of Cost, \"+C+\" and \"+s+\"
\n" ); document.write( "\"+graph%28+500%2C+500%2C+-30%2C+200%2C+-100%2C+600%2C+2x+%2B+20000%2Fx+%29+\"
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