How far is it around a circle?
It is 2p radians. Circumference = 2pr

Since distance = velocity * time, we can say that to go one complete time around,

v*t = 2pr
NOTE:  many books show the "t" as a capital "T" to represent the time for one complete rotation, or PERIOD.
 

Now we can isolate "v" in the equation and insert it into ac = v²/r to get...

ac = 4p²r / T²

Isolate the "r", the  "T", and the "v" to solve various problems.