Question 1031229
The key to understanding the solution is recognize that a diagonal of the square is a diameter of the circle.


{{{pi*r^2=A}}}, and you know A.


Letting d be diameter,
{{{pi*(d/2)^2=A}}}
{{{highlight_green(d^2=4A/pi)}}}
{{{d=2sqrt(A/pi)}}}


Another key to solving is recognize the square is two 45-45-90 special right triangles, and you can use Pythagorean Theorem formula.
Let x be a side of the square.
{{{2x^2=d^2}}}
and you can solve this for x.


This solution almost but not finished, was done purely in symbols, and you can finish.