How do I get the radius of a circle?

Question

How to find the radius of a circle with radius 10 Cm.



I Drew a circle with center O at P(0,0).
Let dr = a small change in radius.
Define Pi = A/(2R) => A = 2PiR

Integrate from R = 0 to R = R
the curve 2Pi ⌠Rdr
= PiR^2 = Area of the circle


So I know the radius is 10 cm...then the area = Pi*100 = 314 cm^2

That seems a bit complex ...I'm just looking for a simple formula for the radius...


I know that if I take an angle of Pi/4 * R = Arc Length of this segment ....so then I tried splitting the area up into 4 pieces

314 /4 = Pi*R

I'm trying to find R ...but I am stuck

Help????

Answer 1

Well if you know the diameter of the circle (one end to the other), divide it in half and you get the radius!

Answer 2

How to find the radius of a circle with radius 10 Cm.

The above statement is of no sense. What are you really trying to find?

If you are trying to find the radius, then
r = C/2pi where C is circumference of circle
r = arc length/theta, where theta is central angle in radians
r = sqrt(A/pi) where A is area of circle.
r = d/2 where d is diameter of circle
etc,etc,etc

Answer 3

You will have to know the diameter, circumference or area of the circle to find the radius.

Radius = Diameter/2
Radius = circumference/2pi
Radius = sqrt(Area/Pi)