def quadratic(a, b, c):
    if a != 0:
        w = b**2 - 4 * a * c
        if w < 0:
            return 'error'
        else:
            x1 = (-b + w**0.5)/(2 * a)
            x2 = (-b - w**0.5)/(2 * a)
            return x1, x2