Question 1038672
{{{A=L*W=4}}}
{{{L=4/W}}}
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A: {{{P=2L+2W=2(L+W)=2(4/W+W)}}}
The width cannot be less than zero but can be as large as you wish so then the perimeter is the same type of function. 
It cannot be less than zero but it can be as large as you wish.
{{{W>0}}}
{{{L>0}}}

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B: As {{{W}}} gets large, {{{4/W->0}}}, so then {{{P}}} looks like a linear function of {{{W}}}
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C: {{{P=2(4/W+W)}}}
Since it's a function of one variable, you can find the derivative to get the minimum value,
{{{dP/dW=-8/W^2+2}}}
{{{(-8/W^2)+2=0}}}
{{{-8/W^2=-2}}}
{{{W^2=4}}}
{{{W=2}}}
So then,
{{{L=4/2}}}
{{{L=2}}}
So the minimum perimeter would be,
{{{P=2(2+2)=8}}}{{{ft}}}