TT GWD 6-30

alexmingzhu

The circle shown has center R.  If arc UST has length 48π, what is the radius of the circle?

 

A.     18

B.     24

C.     32

D.     48

E.      64

I am sorry that I cannot draw the circle here. But I have searched the related discussion and could not figure it out. Can sb tell me why the answer is C?
thanks

assurance

arc UST这段圆弧的周长占整个原周长的3/4(因为剩下的圆弧UT是1/4个圆周)，所以有：

2πr×3/4=48π

解出r=32