#### Answer

The length of a side of the square is $\frac{4}{\pi}$ units.

#### Work Step by Step

Let $A = $ area of the circle
Let $x = $ length of a side of a square
Let $r = $ radius of the circle
$A = \pi r^{2}$
$4x = A$
$r = x$
$4x = \pi r^{2}$
$4x = \pi x^{2}$
$4x - \pi x^{2} = 0$
$x(4-\pi x) = 0$
We find set the factors equal to zero:
$x=0$
$4 - \pi x = 0$
$-\pi x = -4$
$\pi x = 4$
$x = \frac{4}{\pi}$
$x = 0, \frac{4}{\pi}$
We do not consider x=0, for a length of a a side cannot equal 0.
The length of a side of the square is $\frac{4}{\pi}$ units.