What is the radius of a circle with a central angle of 4π7 radians that intercepts an arc of length 12π inches?
The answer is 21 in.
We have
Arc Length = r * theta (in rads) ....so......
12pi = r * (4/7 pi) divide out "pi"
12 = r ( 4/7) multiply both sides by 7/4
12 (7/4) = r = 84/4 = 21 inches
+912 
