import math


def roots_of_quadratic_equation(a, b, c):
    if a == 0:
        if b == 0:
            if c == 0:
                return ['all']
            else:
                return []
        else:
            return [-c / b]
    else:
        if discriminant(a, b, c) > 0:
            return [larger_root(b / a, c / a), smaller_root(b / a, c / a)]
        elif discriminant(a, b, c) == 0:
            return [larger_root(b / a, c / a)]
        else:
            return []


def discriminant(a, b, c):
    return b ** 2 - 4 * a * c


def larger_root(p, q):
    return (-p + math.sqrt(discriminant(1, p, q))) / 2