Question 969085
Area = {{{ 1000 }}} ft2
Let the length parallel to the river  = {{{ y }}} ft
I can say:
{{{ A = x*y }}}
{{{ y = A / x }}}
{{{ y = 1000 / x }}} ft
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The perimeter of the rectangular are is:
{{{ p = 2x + 1000/x  }}}
{{{ C(x) = ( 2x )*8 + ( 1000/x )*5 + 4*25 }}}
{{{ C(x) = 16x + 5000/x + 100 }}}
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{{{ x*y = 1000 }}}
{{{ x }}} can be any number
Also {{{ y }}} can be any number
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The domain is:
0 < C(x) < infinity
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Here's the plot of {{{ C(x) }}}
{{{ graph( 500, 500, -20, 150, -100, 1500, 16x + 5000/x + 100 ) }}}
After the curve takes a dip, it looks like a straight line almost
Hope this helps