Answer: 5.97 cm
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Step-by-step explanation:
Check out the diagram below.
I've defined the following points:
- A = center of the circle, and center of the square
- B, C, D, and E = vertices of the square that are on the circle
- F = midpoint of segment CD
Now focus on triangle ACF. This is an isosceles right triangle with legs of 0.5x each. The hypotenuse is the radius of the circle. Let R be that unknown radius.
The area of the circle is given to us. It is 56 square cm. Use this to find the value of R.

This value is approximate. I used the calculator's stored version of pi to get the most accuracy possible.
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We now know the hypotenuse of triangle ACF.
Use Pythagoras (aka Pythagorean Theorem) to have the following steps:

The final answer is 5.97
With the exception of 0.5 and 0.25, each decimal value mentioned is approximate.
Keep in mind that rounding to 3 sig figs means that we're rounding to 2 decimal places. The units digit is 1 sig fig, and the 2 decimal places give a total of 1+2 = 3 sig figs.
In short, we're rounding to the nearest hundredth.
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Check:
x = 5.97 is the square's side length.
It divides in half to get x/2 = 5.97/2 = 2.985 which gives each leg of triangle ACF.
Use a = 2.985 and b = 2.985 in the Pythagorean Theorem to find that c = 4.22142748 approximately. This is the approximate radius of the circle.
Use that radius to find the area of the circle.
A = pi*r^2
A = pi*(4.22142748)^2
A = 55.984594705958
A = 56.0
I'm rounding the area to 3 sig figs to keep consistent with the rounding done to x. We arrive at the circle area of 56 square cm, which helps confirm the answer is correct.