If we determine the distance from one point to the second point, we get the length of the diameter. This is calculated through the equation,
D= sqrt ((x2 – x1)^2 + (y2 – y1)^2)
Substituting the known values,
D = sqrt ((-1 – 3)^2 + (1 – 3)^2)
D = 4.47
The length of the radius is half that of the diameter. Hence, the radius is,
R = 4.47 /2 = 2.236
Answer: r = 2.24