import math

def cubic(a,b,c):
    q = a*a/9 - b/3
    r = (a*a/27 - b/6)*a + c/2
    s = a/-3
    d = r*r - q*q*q
    if d > 0:
        t = (math.sqrt(d) + abs(r)) ** (1/3)
        u = (t + q/t)
        return s - u if r > 0 else s + u
    else:
        t = math.atan2(math.sqrt(-d), r) / 3
        u = 2 * math.sqrt(q)
        return (
            s - u * math.cos(t),
            s - u * math.cos(t + 2/3*math.pi),
            s - u * math.cos(t - 2/3*math.pi)
        )

print( cubic(10,10,-10) )