Answer:
If by vertices you mean the four corners, as all other possibilities yield indefinite and so infinite circle sizes, then the radius equals half of the hypotenuse of the 45-45-90 Isosceles triangle formed by any two perpendicular sides of the square, as that hypotenuse is equal to the diameter of the circle. Since the side is 20 cm, then the hypotenuse = 20 x sqrt(2) = 28.28. Since the radius is half of that, the answer is 14.1 cm.
Step-by-step explanation:
