Question 1121142
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The area of an equilateral triangle with side length s is {{{(s^2)*(sqrt(3)/4)}}}.<br>
Give that the area of the triangle is 9*sqrt(3), the side length is 6:
{{{(s^2)*(sqrt(3)/4) = 9*sqrt(3)}}}  -->  {{{s^2/4 = 9}}}  -->  s  = 6.<br>
Now find the perimeter of the triangle, which is the same as the perimeter of the square; so you can find the length of a side of the square and then find the length of the diagonal.