



 
Hi Jenn, I am not sure which dimension of the circle is $7'9" = 7.75'$ but I'll show you how to find the side length $s$ of the circle if you know $r,$ the radius. If $h$ is half the the side length if the square as in the diagram then, since triangle ABC is a right triangle Pythagoras' theorem tell us that \[h^2 + h^2 = r^2 \mbox{ or } 2 h^2 = r^2 .\] Thus $s = 2 h = \sqrt{2} r.$ I hope this helps,  


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