def quad_solve(a, b, c):
    if a == 0:
        return False

    D = b*b-4*a*c
    if D < 0:
        return []
    else: 
        x1 = (-b+D**0.5)/2/a
        x2 = (-b-D**0.5)/2/a 
        return [x1, x2]


if __name__ == '__main__':

    print(quad_solve(1,-7, 12))
    print(quad_solve(1, 0, -4))
    print(quad_solve(1, 4, 4))
    print(quad_solve(0, 2, 5))
    print(quad_solve(1, -6, 9))
    print(quad_solve(2, 6, 12))
    print(quad_solve(2, 6, -20))
    print(quad_solve(0.4, 1.4, -3))