Circle passing through P1, P2, P3
Write the coordinates in the boxes.  Then press 
x1 = y1 =
x2 = y2 =
x3 = y3 =

C1 =    C2 =    R =
 R2 =

If you have to put a coefficient using some function symbol (1/5,π,√2,...), put it in a numerical form (calcolatrice)
notes

esempio