find the radius of a circle with circumference of 42.1
You already know the radius.
The director circle of a circle with radius r is a concentric circle with radius r*sqrt(2).
It is twice the radius of a circle
Radius is one-half of the diameter of a circle. Therefore, the radius of an eight-inch diameter circle is four inches. The diameter of a circle is a straight line joining a point on the circumference through the centre to the 'opposite' point on the circumference.
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.
Diameter of a circle = 2*radius Circumference of a circle = 2*radius*pi
The radius of a circle is half its diameter (the measure of the circle from one side across to the other).
Double the radius
the radius is half the diameter
Multiply the radius by 2.