Question 1195290
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The area is 36 square feet, so the side length is {{{sqrt(36) = 6}}} feet.
As a check: 6*6 = 36


Refer to the diagram below.
a = 6, b = 6 are the legs of the right triangle. 
c = hypotenuse
<img src = "https://i.imgur.com/uR8jnus.png">


Apply the pythagorean theorem
{{{a^2+b^2 = c^2}}}


{{{c = sqrt(a^2+b^2)}}}


{{{c = sqrt(6^2+6^2)}}}


{{{c = sqrt(2*6^2)}}}


{{{c = sqrt(2)*sqrt(6^2)}}}


{{{c = sqrt(2)*6}}}


{{{c = 6*sqrt(2)}}}


{{{c = 8.48528}}} approximately


The diagonal is exactly {{{6*sqrt(2)}}} feet long, or approximately 8.48528 feet
Round the decimal value however your teacher instructs.
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