You cannot.
A circle has no mass nor volume and so the concept of density is not appropriate.
Also, the word is radius, not raduis!
Radius (not raduis) =circumference/(2*pi)
Well, if you know the diameter of the circle already, then you can divide it by half to get the radius. If you don't have the diameter however, then you simply have to find the middle of the circle and measure from the middle of the circle to the edge. That would be your radius.
Divide the area by pi. (3.14 or 22/7) Find the square root of your answer. This will be the radius. Multiply the raduis by 2.
If you know the radius place the compass point on a ruler and the pencil end the radius distance away from it. Then put the point on the paper and spin to draw the circle. If you know the diameter divide by two to get the radius and place the compass point on a ruler and the pencil end the radius distance away from it. Then put the point on the paper and spin to draw the circle.
It depends on the values you have. The base of a cylinder is a circle. If you know the circle's diameter, half it to find the radius. If you know the circle's circumference, divide by 2pi to find the radius. If you know the circle's area, divide by pi and take the square root to find the radius.
Surface area = 4*pi*r^2 so r = sqrt[Area/(4*pi)]
If you know the circumference of a circle, you can find the radius by dividing the circumference by the value of Pi (3.14159...)
measure it
The circumference of a circle is the length of the circle's perimeter.
Density = Mass/Volume
Divide the known circumference by pi to find the diameter of the circle.
Area of a circle = pi*radius2