```

if a != 0:
    w=b*b-4*a*c
    if w<0:
        return '方程无解！'         
    else:
        x1 = (-b + math.sqrt(w))/(2*a)
        x2 = (-b - math.sqrt(w))/(2*a)
        return '(%.2f,%.2f)' % (x1,x2)
else:
    x = - c/b
    return '(%.2f)' % x