How can I find the radius of a circle?

How to find the radius of a circle given only a small portion of the circle?

• When given only a small section of a circle (barely even a semicircle) that does not include the center of the circle, how can I determine the radius, diameter, and circumference? I know the formulas, but without the center of the circle, they do no good. Any suggestions?

• Answer:

  If you know the length of the small section of circle, and what portion of the circle that is (i.e. quarter, eighth, half) you can reverse solve to find the radius. the formula to find circumference is pi times diameter. for example, if the section is 10 centimeters long, and thats 1/4 of the circles total you do it backwards. first, you multiply 10 by 4 to get the circumference (40) then, you divide the circumference by pi (3.14). from that you get the diameter (12.74). you then halve that to get the radius (6.37). hope this helps