i don't remember where exactly, i found in internet this image:
i tried to replicate the formula with python and i tried this:
b = 0.9
y = 2*b + sqrt(x*x) + sqrt((x+b)*(3*b-x))
y1 = 2*b + sqrt(x*x) - sqrt((x+b)*(3*b-x))
plot(x,y, x, y1)
where sqrt is the square root!
but my curve is not very similar to the picture.. mayebe i'm not able to read it because of it is handwritten. some help?