Chapter 1 - Equations and Inequalities - 1.5 Applications and Modeling with Quadratic Equations - 1.5 Exercises - Page 132: 37

$10\sqrt{2}$ft

A circle diameter is the same as a square's side length, $x$ and the square's area is $800$ft$^2$ $x^2=800$ $x=\sqrt{800}$ $x=20\sqrt{2}$ Since the radius is half the diameter, the radius of the circle is $10\sqrt{2}$ft