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