The area of a circle with radius r is given by pi * r^2.

Now the area of the circle is given as 13

The radius is sqrt [13/ pi]

= 2.03 ( approximately)

**The required radius is 2.03 **

Given that the area of a circle is 13 square units.

We need to find the radius.

To find the radius, we will use the formula of the area of a circle.

We know that:

A = r^2 * pi such that A is the area of the circle and r is the radius.

Now we will substitute with the values of the area.

==> 13 = r^2 * pi

We know that pi = 22/7 or 3.14

==> 13 = r^2 * 22/7

Now we will multiply by 7/22 both sides.

==> r^2 = 13*7/22 = 4.14 ( approx.)

Now we will take the square root of both sides.

==> r = 2.03

**Then, the radius of the circle whose area is 13 is r = 2.03 units.**