Можно просто параметризировать круг.
t = fixed
x = R * cos(t)
y = R * sin(t)
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Graphics 400, 400, 0, 2
Const R = 30
Const N = 1000
For i = 0 To N
t = Rand(0, 360)
Plot 200 + (Rand(0, R) * Cos(t)), 200 + (Rand(0, R) * Sin(t))
Next
WaitKey()
End